In holding my Gen4 G19, just now, and looking at the place that my hand is (after listening, looking at the many complaints of poor fitting Glock parts to hands) I see that my three fingers on my shooting hand, fit perfectly into the three finger grooves on the front of the grip. The rear of my shooting hand, sticks out below the grip, but just flesh, not bone. About 1/2".
My second finger, fits into the grove Glock fitted to the rear, underside of the trigger guard.
Imagining that being more indented, as some modify that area to need, looks to me as though it would take some of the pressure off the gap between the gap, between the thumb, and rear top knuckle, as in looking at the way my hand fits, seems high and tight to me.
Remember to snip the lower front corner off, at the front of the magazine release, it digs in to my trigger finger.
The wee part in the middle of the trigger, don't press it in, gun will not fire.
This part has two little bars, a MM wide, that keep that part centered.
If you pick your Glock up in a hurray, as from a table, and your trigger finger pushes the trigger sort of into the frame, sideways?
It can jam, and if you do not release the trigger, and put pressure on it again, it jams! The Pistol will not fire.