diff --git a/image_analysis/scale_merge/SearchSpaceGroup.cpp b/image_analysis/scale_merge/SearchSpaceGroup.cpp
index de71f6a7..cc1535a8 100644
--- a/image_analysis/scale_merge/SearchSpaceGroup.cpp
+++ b/image_analysis/scale_merge/SearchSpaceGroup.cpp
@@ -296,11 +296,6 @@ SearchSpaceGroupResult SearchSpaceGroup(
     for (const auto& sg : gemmi::spacegroup_tables::main) {
         if (!sg.is_sohncke() || !sg.is_reference_setting() || RotationSetOf(sg) != best_pg->rotation_set)
             continue;
-        // Centering is a metric property: when the lattice centering is known, only weigh P against
-        // that centering, never a different one.
-        if (opt.lattice_centering != '\0' &&
-            sg.centring_type() != 'P' && sg.centring_type() != opt.lattice_centering)
-            continue;
 
         const gemmi::GroupOps gops = sg.operations();
         SpaceGroupCandidateScore s{.space_group = sg};
@@ -361,13 +356,7 @@ SearchSpaceGroupResult SearchSpaceGroup(
                       return eligible(a);
                   if (a.absent_observed != b.absent_observed)
                       return a.absent_observed > b.absent_observed;
-                  // Tie: prefer the metric centering, then the lower space-group number.
-                  if (opt.lattice_centering != '\0') {
-                      const bool am = a.space_group.centring_type() == opt.lattice_centering;
-                      const bool bm = b.space_group.centring_type() == opt.lattice_centering;
-                      if (am != bm)
-                          return am;
-                  }
+                  // Tie (e.g. I23 vs I2_13, indistinguishable by absences): lower space-group number.
                   return a.space_group.number < b.space_group.number;
               });
 
diff --git a/image_analysis/scale_merge/SearchSpaceGroup.h b/image_analysis/scale_merge/SearchSpaceGroup.h
index e65c7e24..acdb0286 100644
--- a/image_analysis/scale_merge/SearchSpaceGroup.h
+++ b/image_analysis/scale_merge/SearchSpaceGroup.h
@@ -50,10 +50,10 @@ struct SearchSpaceGroupOptions {
     // symmetry than the intensities support. Unset = search every Sohncke system.
     std::optional<gemmi::CrystalSystem> lattice_system;
 
-    // Lattice centering from LatticeSearch ('P','C','I','F','R'; '\0' = unknown). Centering is a
-    // metric property of the lattice, so when known the space-group search only weighs P vs this
-    // centering and prefers the metric one when the data cannot decide between them.
-    char lattice_centering = '\0';
+    // Centering is NOT taken from the lattice metric: an indexer that returns the conventional cell
+    // (e.g. cubic 'P'-looking axes for a body-centered lattice) hides the centering, which lives only
+    // in the systematic absences. Stage B therefore tests every centering allowed by the point group
+    // and confirms it from the data (h+k+l etc. absent), rather than trusting a geometric hint.
 
     // Friedel mates are treated as equivalent when matching HKLs (i.e. anomalous signal ignored).
     bool merge_friedel = true;
diff --git a/process/JFJochProcess.cpp b/process/JFJochProcess.cpp
index 60188557..8b2c46c9 100644
--- a/process/JFJochProcess.cpp
+++ b/process/JFJochProcess.cpp
@@ -481,11 +481,9 @@ ProcessResult JFJochProcess::Run(JFJochProcessObserver *observer) {
             sg_opts.merge_friedel = experiment_.GetScalingSettings().GetMergeFriedel();
             sg_opts.d_min_limit_A = experiment_.GetScalingSettings().GetHighResolutionLimit_A().value_or(0.0);
             // Constrain the search to subgroups of the lattice (metric) symmetry found by rotation
-            // indexing, and weigh centering only against the metric one.
-            if (end_msg.rotation_lattice_type.has_value()) {
+            // indexing. Centering is not constrained here - it is determined from the absences.
+            if (end_msg.rotation_lattice_type.has_value())
                 sg_opts.lattice_system = end_msg.rotation_lattice_type->crystal_system;
-                sg_opts.lattice_centering = end_msg.rotation_lattice_type->centering;
-            }
             const auto sg_search = SearchSpaceGroup(sm.merged, sg_opts);
             stats_text << SearchSpaceGroupResultToText(sg_search) << "\n\n";
 
diff --git a/tools/jfjoch_process.cpp b/tools/jfjoch_process.cpp
index 9a1001f9..38c4085e 100644
--- a/tools/jfjoch_process.cpp
+++ b/tools/jfjoch_process.cpp
@@ -679,8 +679,11 @@ int main(int argc, char **argv) {
     experiment.ImagesPerTrigger(images_to_process);
     experiment.NumTriggers(1);
 
-    if (fixed_reference_unit_cell.has_value())
-        experiment.SetUnitCell(*fixed_reference_unit_cell);
+    // Re-determine the unit cell from scratch: discard any cell stored in the input file so
+    // indexing is not biased by it. A stale or wrong stored cell otherwise resolves the indexing
+    // algorithm to FFBIDX and drives it to the wrong lattice (e.g. a non-cubic cell for cubic
+    // insulin). A user-supplied -C cell still takes effect (clears to nullopt when absent).
+    experiment.SetUnitCell(fixed_reference_unit_cell);
 
     if (max_spot_count_override.has_value()) {
         experiment.MaxSpotCount(max_spot_count_override.value());