diff --git a/rugnux/Rugnux.cpp b/rugnux/Rugnux.cpp
index 5ceb6a80..242b60ee 100644
--- a/rugnux/Rugnux.cpp
+++ b/rugnux/Rugnux.cpp
@@ -594,12 +594,12 @@ ProcessResult Rugnux::Run(RugnuxObserver *observer) {
             // running merge with ScaleOnTheFly (fixed partiality), then merge directly. With an external
             // reference each image is already scaled against it during the per-image pass, so skip.
             if (config_.reference_data.empty()) {
-                for (int i = 0; i < config_.scaling_iter; i++) {
-                    phase("Scaling images (" + label + ", iteration " + std::to_string(i + 1) + "/"
-                          + std::to_string(config_.scaling_iter) + ")");
-                    auto merge_result = MergeAll(experiment_, indexer->GetIntegrationOutcome(), false);
-                    indexer->ScaleAllImages(merge_result);
-                }
+                // One pass: the per-image scale G is the exact one-pass solution, so iterating only
+                // rebuilds the reference from the freshly-scaled (noisy) data - degrading weak stills
+                // instead of converging (measured CC1/2 collapse at the default 3 iters on weak data).
+                phase("Scaling images (" + label + ")");
+                auto merge_result = MergeAll(experiment_, indexer->GetIntegrationOutcome(), false);
+                indexer->ScaleAllImages(merge_result);
             }
             const std::vector<IntegrationOutcome> &merge_input = indexer->GetIntegrationOutcome();
 
diff --git a/rugnux/rugnux_cli.cpp b/rugnux/rugnux_cli.cpp
index fa417766..78cde433 100644
--- a/rugnux/rugnux_cli.cpp
+++ b/rugnux/rugnux_cli.cpp
@@ -1035,7 +1035,12 @@ int main(int argc, char **argv) {
             merged_statistics = std::move(r.statistics);
             error_model_isa = r.isa;
         } else {
-            for (int i = 0; i < scaling_iter; i++) {
+            // The per-image scale G is the exact one-pass solution (Scale re-solves from raw I and never
+            // reads the prior correction), so with a self-rebuilt reference iterating only re-fits the
+            // freshly-scaled noise and degrades weak stills (measured CC1/2 collapse at the default 3
+            // iters). Scale the self-reference merge once; a fixed external reference keeps scaling_iter.
+            const int n_self = reference_data.empty() ? 1 : scaling_iter;
+            for (int i = 0; i < n_self; i++) {
                 if (reference_data.empty())
                     ScaleOnTheFly(experiment, MergeAll(experiment, reflections)).Scale(reflections, nthreads);
                 else