diff --git a/cases/disk_buffer_crash_performance/configs/axosyslog.conf b/cases/disk_buffer_crash_performance/configs/axosyslog.conf
index 341e925..292b4c1 100644
--- a/cases/disk_buffer_crash_performance/configs/axosyslog.conf
+++ b/cases/disk_buffer_crash_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -14,6 +17,7 @@ destination d_tcp {
         port(9001)
         disk-buffer(
             reliable(yes)
+            prealloc(yes)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -23,4 +27,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/disk_buffer_performance/configs/axosyslog.conf b/cases/disk_buffer_performance/configs/axosyslog.conf
index 2301707..24d3cf1 100644
--- a/cases/disk_buffer_performance/configs/axosyslog.conf
+++ b/cases/disk_buffer_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -14,6 +17,8 @@ destination d_tcp {
         port(9001)
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -23,4 +28,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/disk_buffer_persistence_correctness/configs/axosyslog.conf b/cases/disk_buffer_persistence_correctness/configs/axosyslog.conf
index e3e8f3f..e459a83 100644
--- a/cases/disk_buffer_persistence_correctness/configs/axosyslog.conf
+++ b/cases/disk_buffer_persistence_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -15,6 +18,8 @@ destination d_tcp {
         template("${MESSAGE}\n")
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -24,4 +29,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/file_rotate_create_correctness/configs/axosyslog.conf b/cases/file_rotate_create_correctness/configs/axosyslog.conf
index 6afebcf..38a806a 100644
--- a/cases/file_rotate_create_correctness/configs/axosyslog.conf
+++ b/cases/file_rotate_create_correctness/configs/axosyslog.conf
@@ -6,6 +6,8 @@ source s_file {
         filename-pattern("*.log*")
         flags(no-parse)
         follow-freq(0.1)
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
     );
 };
 
@@ -19,4 +21,5 @@ destination d_tcp {
 log {
     source(s_file);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/file_rotate_restart_correctness/configs/axosyslog.conf b/cases/file_rotate_restart_correctness/configs/axosyslog.conf
index a021293..0ad29e0 100644
--- a/cases/file_rotate_restart_correctness/configs/axosyslog.conf
+++ b/cases/file_rotate_restart_correctness/configs/axosyslog.conf
@@ -12,6 +12,8 @@ source s_file {
         filename-pattern("*.log*")
         flags(no-parse)
         follow-freq(0.1)
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         recursive(no)
     );
 };
@@ -27,4 +29,5 @@ destination d_tcp {
 log {
     source(s_file);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/file_rotate_truncate_correctness/configs/axosyslog.conf b/cases/file_rotate_truncate_correctness/configs/axosyslog.conf
index 6afebcf..38a806a 100644
--- a/cases/file_rotate_truncate_correctness/configs/axosyslog.conf
+++ b/cases/file_rotate_truncate_correctness/configs/axosyslog.conf
@@ -6,6 +6,8 @@ source s_file {
         filename-pattern("*.log*")
         flags(no-parse)
         follow-freq(0.1)
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
     );
 };
 
@@ -19,4 +21,5 @@ destination d_tcp {
 log {
     source(s_file);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/file_to_tcp_performance/configs/axosyslog.conf b/cases/file_to_tcp_performance/configs/axosyslog.conf
index 6afebcf..38a806a 100644
--- a/cases/file_to_tcp_performance/configs/axosyslog.conf
+++ b/cases/file_to_tcp_performance/configs/axosyslog.conf
@@ -6,6 +6,8 @@ source s_file {
         filename-pattern("*.log*")
         flags(no-parse)
         follow-freq(0.1)
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
     );
 };
 
@@ -19,4 +21,5 @@ destination d_tcp {
 log {
     source(s_file);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/file_truncate_correctness/configs/axosyslog.conf b/cases/file_truncate_correctness/configs/axosyslog.conf
index 6e2f8b3..768b325 100644
--- a/cases/file_truncate_correctness/configs/axosyslog.conf
+++ b/cases/file_truncate_correctness/configs/axosyslog.conf
@@ -5,6 +5,8 @@ source s_file {
         "/data/input.log"
         flags(no-parse)
         follow-freq(0.1)
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
     );
 };
 
@@ -18,4 +20,5 @@ destination d_tcp {
 log {
     source(s_file);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/otlp_grpc_to_otlp_grpc_correctness/configs/axosyslog.conf b/cases/otlp_grpc_to_otlp_grpc_correctness/configs/axosyslog.conf
index 26b2896..0283d01 100644
--- a/cases/otlp_grpc_to_otlp_grpc_correctness/configs/axosyslog.conf
+++ b/cases/otlp_grpc_to_otlp_grpc_correctness/configs/axosyslog.conf
@@ -17,6 +17,8 @@
 source s_otlp {
     opentelemetry(
         port(4317)
+        workers({{.CPUs}})
+        concurrent-requests(4)
     );
 };
 
@@ -29,4 +31,5 @@ destination d_otlp {
 log {
     source(s_otlp);
     destination(d_otlp);
+    flags(flow-control);
 };
diff --git a/cases/otlp_grpc_to_otlp_grpc_performance/configs/axosyslog.conf b/cases/otlp_grpc_to_otlp_grpc_performance/configs/axosyslog.conf
index 26b2896..0283d01 100644
--- a/cases/otlp_grpc_to_otlp_grpc_performance/configs/axosyslog.conf
+++ b/cases/otlp_grpc_to_otlp_grpc_performance/configs/axosyslog.conf
@@ -17,6 +17,8 @@
 source s_otlp {
     opentelemetry(
         port(4317)
+        workers({{.CPUs}})
+        concurrent-requests(4)
     );
 };
 
@@ -29,4 +31,5 @@ destination d_otlp {
 log {
     source(s_otlp);
     destination(d_otlp);
+    flags(flow-control);
 };
diff --git a/cases/real_world_1_performance/configs/axosyslog.conf b/cases/real_world_1_performance/configs/axosyslog.conf
index 9a7ca6e..b47697d 100644
--- a/cases/real_world_1_performance/configs/axosyslog.conf
+++ b/cases/real_world_1_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(syslog-protocol)
     );
 };
@@ -32,4 +35,5 @@ log {
         rewrite(r_mark_dropped);
     };
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/regex_mask_performance/configs/axosyslog.conf b/cases/regex_mask_performance/configs/axosyslog.conf
index 3958cbd..0167638 100644
--- a/cases/regex_mask_performance/configs/axosyslog.conf
+++ b/cases/regex_mask_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -23,4 +26,5 @@ log {
     source(s_tcp);
     rewrite(r_mask_conn);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/set_field_performance/configs/axosyslog.conf b/cases/set_field_performance/configs/axosyslog.conf
index 068359a..9873890 100644
--- a/cases/set_field_performance/configs/axosyslog.conf
+++ b/cases/set_field_performance/configs/axosyslog.conf
@@ -7,6 +7,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -26,4 +29,5 @@ log {
     source(s_tcp);
     rewrite(r_set);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/sighup_correctness/configs/axosyslog.conf b/cases/sighup_correctness/configs/axosyslog.conf
index b0bd6c7..2023e08 100644
--- a/cases/sighup_correctness/configs/axosyslog.conf
+++ b/cases/sighup_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -19,4 +22,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/syslog_parsing_performance/configs/axosyslog.conf b/cases/syslog_parsing_performance/configs/axosyslog.conf
index 05714e5..d166a08 100644
--- a/cases/syslog_parsing_performance/configs/axosyslog.conf
+++ b/cases/syslog_parsing_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(syslog-protocol)
     );
 };
@@ -18,4 +21,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_blackhole_performance/configs/axosyslog.conf b/cases/tcp_to_blackhole_performance/configs/axosyslog.conf
index 50b5cc3..63cccb2 100644
--- a/cases/tcp_to_blackhole_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_blackhole_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -15,4 +18,5 @@ destination d_null {
 log {
     source(s_tcp);
     destination(d_null);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_http_5min_performance/configs/axosyslog.conf b/cases/tcp_to_http_5min_performance/configs/axosyslog.conf
index 3ec10c2..d3e18ab 100644
--- a/cases/tcp_to_http_5min_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_http_5min_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -13,7 +16,7 @@ destination d_http {
         url("http://receiver:9001/")
         method("POST")
         body("${MESSAGE}")
-        workers(4)
+        workers({{.CPUs}})
         batch-lines(1000)
         batch-timeout(100)
     );
@@ -22,4 +25,5 @@ destination d_http {
 log {
     source(s_tcp);
     destination(d_http);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_http_performance/configs/axosyslog.conf b/cases/tcp_to_http_performance/configs/axosyslog.conf
index 3ec10c2..d3e18ab 100644
--- a/cases/tcp_to_http_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_http_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -13,7 +16,7 @@ destination d_http {
         url("http://receiver:9001/")
         method("POST")
         body("${MESSAGE}")
-        workers(4)
+        workers({{.CPUs}})
         batch-lines(1000)
         batch-timeout(100)
     );
@@ -22,4 +25,5 @@ destination d_http {
 log {
     source(s_tcp);
     destination(d_http);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_http_persistent_correctness/configs/axosyslog.conf b/cases/tcp_to_http_persistent_correctness/configs/axosyslog.conf
index 4e45500..c7e6398 100644
--- a/cases/tcp_to_http_persistent_correctness/configs/axosyslog.conf
+++ b/cases/tcp_to_http_persistent_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -13,11 +16,13 @@ destination d_http {
         url("http://receiver:9001/")
         method("POST")
         body("${MESSAGE}")
-        workers(4)
+        workers({{.CPUs}})
         batch-lines(1000)
         batch-timeout(100)
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -27,4 +32,5 @@ destination d_http {
 log {
     source(s_tcp);
     destination(d_http);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_5min_performance/configs/axosyslog.conf b/cases/tcp_to_tcp_5min_performance/configs/axosyslog.conf
index 5b0c799..2f78a92 100644
--- a/cases/tcp_to_tcp_5min_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_5min_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -18,4 +21,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_performance/configs/axosyslog.conf b/cases/tcp_to_tcp_performance/configs/axosyslog.conf
index 5b0c799..2f78a92 100644
--- a/cases/tcp_to_tcp_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -18,4 +21,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_persistent_correctness/configs/axosyslog.conf b/cases/tcp_to_tcp_persistent_correctness/configs/axosyslog.conf
index e3e8f3f..e459a83 100644
--- a/cases/tcp_to_tcp_persistent_correctness/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_persistent_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -15,6 +18,8 @@ destination d_tcp {
         template("${MESSAGE}\n")
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -24,4 +29,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_persistent_crash_correctness/configs/axosyslog.conf b/cases/tcp_to_tcp_persistent_crash_correctness/configs/axosyslog.conf
index abf9839..c06f060 100644
--- a/cases/tcp_to_tcp_persistent_crash_correctness/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_persistent_crash_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -15,6 +18,7 @@ destination d_tcp {
         template("${MESSAGE}\n")
         disk-buffer(
             reliable(yes)
+            prealloc(yes)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -24,4 +28,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_persistent_performance/configs/axosyslog.conf b/cases/tcp_to_tcp_persistent_performance/configs/axosyslog.conf
index 2301707..24d3cf1 100644
--- a/cases/tcp_to_tcp_persistent_performance/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_persistent_performance/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -14,6 +17,8 @@ destination d_tcp {
         port(9001)
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -23,4 +28,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/tcp_to_tcp_persistent_restart_correctness/configs/axosyslog.conf b/cases/tcp_to_tcp_persistent_restart_correctness/configs/axosyslog.conf
index e3e8f3f..e459a83 100644
--- a/cases/tcp_to_tcp_persistent_restart_correctness/configs/axosyslog.conf
+++ b/cases/tcp_to_tcp_persistent_restart_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -15,6 +18,8 @@ destination d_tcp {
         template("${MESSAGE}\n")
         disk-buffer(
             reliable(no)
+            prealloc(yes)
+            front-cache-size(10000)
             capacity-bytes(4294967296)
             dir("/var/lib/syslog-ng/disk-buffer/")
         )
@@ -24,4 +29,5 @@ destination d_tcp {
 log {
     source(s_tcp);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/cases/wrapped_json_correctness/configs/axosyslog.conf b/cases/wrapped_json_correctness/configs/axosyslog.conf
index ba37136..19c8109 100644
--- a/cases/wrapped_json_correctness/configs/axosyslog.conf
+++ b/cases/wrapped_json_correctness/configs/axosyslog.conf
@@ -4,6 +4,9 @@ source s_tcp {
     tcp(
         ip("0.0.0.0")
         port(9000)
+        max-connections({{.Connections}})
+        log-iw-size({{.Connections}}000)
+        log-fetch-limit(1000)
         flags(no-parse)
     );
 };
@@ -24,4 +27,5 @@ log {
     source(s_tcp);
     parser(p_json);
     destination(d_tcp);
+    flags(flow-control);
 };
diff --git a/internal/orchestrator/docker.go b/internal/orchestrator/docker.go
index c421ec7..e5be767 100644
--- a/internal/orchestrator/docker.go
+++ b/internal/orchestrator/docker.go
@@ -36,6 +36,67 @@ func resolveGeneratorConnections(explicit int) int {
 	return 3
 }
 
+// totalGeneratorConnections reports how many parallel connections the
+// generator(s) will open to the subject this run, summing across all
+// generators in multi-generator mode (they all fan in to the same subject).
+func totalGeneratorConnections(tc *config.TestCase) int {
+	if tc.MultiGenerator() {
+		total := 0
+		for _, g := range tc.Generators {
+			total += resolveGeneratorConnections(g.Connections)
+		}
+		return total
+	}
+	return resolveGeneratorConnections(tc.Generator.Connections)
+}
+
+// configTemplateContext is the data exposed to a subject config rendered as a
+// Go text/template. It carries only generic facts about the run — never a
+// subject's tuning vocabulary — so a config adapts itself to the workload
+// (e.g. AxoSyslog sizes max-connections() to the generator fan-out, or an
+// OpenTelemetry source sets workers() to the CPU count).
+type configTemplateContext struct {
+	// Connections is the total number of parallel connections the
+	// generator(s) will open to the subject this run.
+	Connections int
+	// CPUs is the host CPU count.
+	CPUs int
+}
+
+// renderSubjectConfig renders the subject config at srcPath as a Go
+// text/template when it contains template actions ("{{"), writing the result
+// into tmpDir and returning the rendered file's path. Configs with no template
+// actions, directory-form configs (e.g. cribl-stream), and missing paths are
+// returned unchanged — so non-templated subjects, and the existing
+// missing-path tolerance, are unaffected.
+func renderSubjectConfig(srcPath, tmpDir string, ctx configTemplateContext) (string, error) {
+	info, err := os.Stat(srcPath)
+	if err != nil || info.IsDir() {
+		return srcPath, nil
+	}
+	raw, err := os.ReadFile(srcPath)
+	if err != nil {
+		return "", err
+	}
+	if !strings.Contains(string(raw), "{{") {
+		return srcPath, nil
+	}
+	tmpl, err := template.New(filepath.Base(srcPath)).Parse(string(raw))
+	if err != nil {
+		return "", fmt.Errorf("parsing config template %s: %w", srcPath, err)
+	}
+	outPath := filepath.Join(tmpDir, filepath.Base(srcPath))
+	f, err := os.Create(outPath)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	if err := tmpl.Execute(f, ctx); err != nil {
+		return "", fmt.Errorf("rendering config template %s: %w", srcPath, err)
+	}
+	return outPath, nil
+}
+
 const composeTemplate = `# Auto-generated by harness — do not edit
 networks:
   bench:
@@ -690,9 +751,19 @@ func writeCompose(path string, cfg RunConfig) error {
 	tc := cfg.TestCase
 	s := cfg.Subject
 
+	// Render the subject config as a template (opt-in via {{...}}) so it can
+	// adapt to the run's connection/CPU counts.
+	renderedConfigSrc, err := renderSubjectConfig(cfg.ConfigSrcPath, cfg.TmpDir, configTemplateContext{
+		Connections: totalGeneratorConnections(tc),
+		CPUs:        runtime.NumCPU(),
+	})
+	if err != nil {
+		return err
+	}
+
 	// Docker Compose on Windows needs forward slashes in volume paths;
 	// backslashes are interpreted as YAML escape sequences inside quoted strings.
-	configSrc := filepath.ToSlash(cfg.ConfigSrcPath)
+	configSrc := filepath.ToSlash(renderedConfigSrc)
 	tmpDir := filepath.ToSlash(cfg.TmpDir)
 
 	subjectContainer := "bench-subject-" + s.Name