The correlation stage kept only reflections with I/sigma >= present_i_over_sigma
(3.0). That statistic is taken on the P1-MERGED intensities, whose sigma is
floored at b|I| (Merge.h, SigmaWithSystematicFloor) so that ISa = 1/b is the
asymptotic I/sigma ceiling - no reflection in a merge can read above it.
Verified over the rotation battery: max I/sigma equals 1/b on every merge.
So a fixed cut is not a per-reflection test at all. Every reflection sitting at
the floor reads 1/b exactly, however strong, and on a merge whose ISa falls
below the cut NOTHING passes: every operator is left with no pairs, its CC is
NaN, and the point group collapses to 1. The predicate "search-merge ISa < 3"
identifies the affected crystals exactly.
It is latent today - no crystal in the battery starves on the shipped
integration background - but it fires on four as soon as an additive intensity
bias is removed, and it is not a data-quality verdict: the crystals it silences
have final merges at ISa 19-22 while their low-multiplicity search merge sits
at 3.5-4.0, just above the cut.
Cap the cut at the merge's own I/sigma quantile so the correlation stage always
keeps at least its strongest quarter. A no-op wherever the fixed cut already
keeps that many - the cut stays exactly 3.000 on healthy merges. Battery
unchanged at 34 space groups matching XDS / 3 differing, with merged
observations identical to 0.000% on all 37 crystals.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
8ecd126e93