At the Small Arms School, during the later 20 years or so, pistol users were pretty-well taught several ways to shoot but it was left to them as to which method they preferred....., so long as it was safe and they could safely undertake all of the drills that were required.
I used to shoot it, held in the usual way, right handed, arm slightly bent, but cupped at the bottom of the mag/grip with the left hand so that the right thumb nail was sort of held onto the grip by the left thumb. Not quite one of the grips taught but close enough. Nobody ever used to say anything toooo detrimental