Intent of the flagged thumb in high pectoral?
Why the flagged thumb in the high pectoral retention shooting position?
Is the primary reason related to directing the muzzle for safety? Point of aim?
Or perhaps to assist clearing the slide's recoil path?
Looking for the background here for a revolver shooter. It seems a more secure grip with the thumb closed down would be better for retention and recoil control thus suggesting a modification of the common technique. My limited searches have not unearthed this particular "why" question yet.