diff --git a/image_analysis/scale_merge/Merge.cpp b/image_analysis/scale_merge/Merge.cpp
index 7a196d05..dd5aae6d 100644
--- a/image_analysis/scale_merge/Merge.cpp
+++ b/image_analysis/scale_merge/Merge.cpp
@@ -474,9 +474,6 @@ std::vector<char> MergeOnTheFly::DeltaCChalfReject(const std::vector<Integration
     std::unordered_map<uint64_t, Acc> acc;
     std::vector<int> img_half(outcomes.size(), 0);
 
-    std::mt19937 lrng{2026061600u};
-    std::bernoulli_distribution hd{0.5};
-
     // ---- pass 1: accumulate half-set sums, record each image's half ----
     auto contribution = [&](const Reflection &r, uint64_t &key, double &wI, double &w) -> bool {
         if (generator.IsSystematicallyAbsent(r)) return false;
@@ -493,7 +490,9 @@ std::vector<char> MergeOnTheFly::DeltaCChalfReject(const std::vector<Integration
     };
 
     for (size_t i = 0; i < outcomes.size(); ++i) {
-        const int half = hd(lrng) ? 1 : 0;
+        // Same deterministic half-set as the merge (HalfForImage), so deltaCChalf is measured on the
+        // exact CC1/2 split the statistics report - not an independent, order-dependent RNG draw.
+        const int half = HalfForImage(static_cast<int64_t>(i));
         img_half[i] = half;
         for (const auto &r : outcomes[i].reflections) {
             uint64_t key; double wI, w;