diff --git a/image_analysis/scale_merge/SearchSpaceGroup.cpp b/image_analysis/scale_merge/SearchSpaceGroup.cpp
index fe61e95e..a355c281 100644
--- a/image_analysis/scale_merge/SearchSpaceGroup.cpp
+++ b/image_analysis/scale_merge/SearchSpaceGroup.cpp
@@ -517,7 +517,6 @@ SearchSpaceGroupResult SearchSpaceGroup(
         // (imperfectly scaled data) and VETOES a twin whose chi^2 now looks self-consistent but whose b
         // balloons - the chi^2 ratio alone no longer separates them.
         double parent_b = -1.0;
-        const PointGroupInfo *parent_pg = nullptr;
         // Every confirmed subgroup of the largest order below this candidate. There can be more than one
         // - 422 has both 4 and 222 - and on a twinned crystal the rival is not a harmless alternative: a
         // P4 crystal twinned by 2[100] has its two twin 2-folds confirmed, so 222 is CC-confirmed too and
@@ -535,8 +534,13 @@ SearchSpaceGroupResult SearchSpaceGroup(
                     if (s.order > parent_order) {
                         parent_order = s.order;
                         parent_b = s.b_extra;
-                        parent_pg = s.pg;
                         parents.clear();
+                    } else {
+                        // Tied parent. The b tests answer to the most damning of them, exactly as the H
+                        // test below does: the SMALLEST parent b is the one that makes the veto easiest to
+                        // trip and the rescue hardest to pass, and a rival subgroup that already contains
+                        // the twin laws has its own b ballooned - taking it would hide the twin.
+                        parent_b = std::min(parent_b, s.b_extra);
                     }
                     parents.push_back(s.pg);
                 }
@@ -611,8 +615,11 @@ SearchSpaceGroupResult SearchSpaceGroup(
                                 + "x the parent's (bound " + FormatDouble(opt.max_operator_h_ratio, 2)
                                 + ") - the added operator relates unequal intensities, as a twin law does";
                 else if (b_refused)
+                    // Against the FLOORED parent b, which is what the test compared - quoting the raw
+                    // parent b reads as a far bigger balloon than the one that actually tripped the veto.
                     refused_why = "its merge's systematic error b is " + FormatDouble(c.b_extra, 3)
-                                + " against the subgroup's " + FormatDouble(parent_b, 3)
+                                + " against the subgroup's "
+                                + FormatDouble(std::max(parent_b, opt.min_systematic_b_for_veto), 3)
                                 + " (bound " + FormatDouble(opt.max_systematic_b_veto, 2)
                                 + "x) - the added operator forces unequal intensities together";
                 else if (std::isfinite(c.chi2) && std::isfinite(chi2_ref))