diff --git a/scripts/ka-close-matrix.sh b/scripts/ka-close-matrix.sh
index 3132e95..30d7691 100755
--- a/scripts/ka-close-matrix.sh
+++ b/scripts/ka-close-matrix.sh
@@ -144,8 +144,10 @@ run_causal() { # $1=mode $2=port
 # ---- matrix --------------------------------------------------------------
 run_plain  ka    "$BASE_PORT"
 run_plain  close "$((BASE_PORT + 1))"
-run_causal ka    "$((BASE_PORT + 2))"
-run_causal close "$((BASE_PORT + 3))"
+if [ "${PLAIN_ONLY:-0}" != 1 ]; then
+  run_causal ka    "$((BASE_PORT + 2))"
+  run_causal close "$((BASE_PORT + 3))"
+fi
 
 # ---- summary -------------------------------------------------------------
 say "=== SUMMARY ==="