A spot that outgrows the r1 disk is summed over its measured footprint ellipse and its background
ring starts beyond it. That reach was the same 3 sigma that decides whether the spot outgrew the
disk at all. Wide spots are not Gaussian - mosaic streaks and diffuse halos carry flux past 3 sigma -
so the ring started on the spot's own tails and read them as background.
The install test stays at 3 sigma (BRAGG_FOOTPRINT_NSIGMA); the new BRAGG_FOOTPRINT_REACH = 4 sets
how far the summation ellipse, the ring start and the profile grid go. Compact protein spots never
install the footprint, so they are unchanged bit for bit.
Evidence (rugnux's own combined fulls put through XDS's own per-observation corrections, so only
the integration differs; SHELXL R1(>4sig) on ~93% of observations matched to XDS by hkl):
citric acid: 3 sigma .0521, 4 sigma .0519, 5 sigma .0526 (XDS 3D summation .0484)
HEPES: 3 sigma .0348, 4 sigma .0338, 5 sigma .0344 (XDS .0311)
Full pipeline SHELXL R1: citric .0697 -> .0685, HEPES .0405 -> .0370.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K5K8jvPPbmCrbqnWkddTuB
leonarski_fandClaude Opus 5.5
a498e8f8e0