diff --git a/image_analysis/scale_merge/ScaleOnTheFly.cpp b/image_analysis/scale_merge/ScaleOnTheFly.cpp
index 7c719436..de9db0be 100644
--- a/image_analysis/scale_merge/ScaleOnTheFly.cpp
+++ b/image_analysis/scale_merge/ScaleOnTheFly.cpp
@@ -148,9 +148,15 @@ void ScaleOnTheFly::Scale(IntegrationOutcome &integration_outcome) const {
 // A per-image scale that has collapsed toward zero multiplies that image's intensities by 1/G - and its
 // sigmas by the same factor, so nothing downstream can recognise it: the merge's n-sigma outlier test
 // scales with the very number that is wrong. The rotation path already refuses a per-frame scale this
-// far below its neighbours; the stills path had no such guard. An image whose fit collapsed is left
-// UNSCALED (G = 1, the same state as an image with too few reflections to fit) rather than merged with
-// its intensities blown up.
+// far below its neighbours; the stills path had no such guard.
+//
+// Such an image is DROPPED from the merge, not merged unscaled. Substituting G = 1 looks conservative
+// but is the more damaging of the two errors: if the collapsed value was a failed fit, the image goes in
+// mis-scaled by an unknown factor, and if it was a real scale (per-crystal scales on serial stills
+// genuinely span orders of magnitude, unlike frames of one rotation sweep) then G = 1 divides both its
+// intensities AND its sigmas by 1/G, so it enters at 1/G^2 times the weight it deserves - the merge
+// cannot down-weight it, because the number that is wrong is the same number the weight is built from.
+// An image whose scale is not believable has no usable scale, so it contributes nothing instead.
 void ScaleOnTheFly::RejectCollapsedScales(std::vector<IntegrationOutcome> &integration) {
     std::vector<double> fitted;
     fitted.reserve(integration.size());
@@ -168,10 +174,10 @@ void ScaleOnTheFly::RejectCollapsedScales(std::vector<IntegrationOutcome> &integ
     for (auto &i: integration) {
         if (!i.image_scale_g || !std::isfinite(*i.image_scale_g) || *i.image_scale_g >= g_floor)
             continue;
+        // A non-finite correction is what every merge path already skips on (Merge.cpp), so this drops
+        // the image consistently from the merged intensities, the error model and the statistics.
         for (auto &r: i.reflections)
-            r.image_scale_corr = (std::isfinite(r.rlp) && r.partiality > 0.0f)
-                                     ? static_cast<float>(r.rlp / r.partiality)
-                                     : NAN;
+            r.image_scale_corr = NAN;
         i.image_scale_cc.reset();
         i.image_scale_cc_n.reset();
         i.image_scale_g.reset();
@@ -179,8 +185,8 @@ void ScaleOnTheFly::RejectCollapsedScales(std::vector<IntegrationOutcome> &integ
     }
     if (n_rejected > 0)
         Logger("ScaleOnTheFly").Warning(
-            "Left {} image(s) unscaled: their per-image scale collapsed more than {:.0f}x below the "
-            "run median, which would have amplified their intensities by the same factor",
+            "Dropped {} image(s) from the merge: their per-image scale collapsed more than {:.0f}x below "
+            "the run median, so it is not a scale the intensities can be put on",
             n_rejected, 1.0 / MIN_CREDIBLE_SCALE_RATIO);
 }