Well, I'm not an expert on armor, but as I recall it's rounded at the belly and not at the shoulders, and the hole goes all the way through.
Yep. That's where the soft, squishy parts are that need area to move. Armor too close against the belly restricts your diaphram, making breathing difficult.
There is a set of armor for Henry VIII, IIRC, that has two proof marks. One is a dent, then a through hole a couple of inches away.