John, scale = 2 (EDIT with Th=0) , in GamMac WILL see all pixels (even a single) as affecting min/max, avoid noise pixels by eg denoise on DC clip,
with a perfect source that may be what you want, with less than prefect, needs more effort.
@ Lem, GamMac never was intended to be any kind of one suit fits all, merely a pre tweak easy get in sync type of thing.
If we all had Lem at our sides, GamMac would be of little worth.
John, seek Lem's counsil, he seems to be the man