At the end of the day, I still think that a 6" circle directly at the midline seems to be a perfectly adequate target for training purposes. In the spirit of the Mozambique drill/failure drill, shoot for center of mass; if it works, great; if not, the head is a better target if available.
just to clarify, this statement was intended to mean that I've simply never seen a facial GSW in person; not that they aren't survivable, by any means.