It was a matter of tension, across the back of the hand especially. Adds to a cleaner release and less of a tendency to pluck the string off arrow line.
It is really part of a shooting system, draw the arrow straight back, hit your first anchor point, finger on the corner of your mouth, then continue drawing back hitting your second anchor point with your thumb along your jaw wherever it feels best to you.
Continue the push, pull back as you release in a close to straight line with your arrow.
The slight head tilt lays your arrow directly under your dominant eye and closes the gap between the angle your eye is looking at the target and what angle your arrow is at.
It really is an incredible but simple system, beautiful in execution and deadly accurate.
It can be used as a instinctive type of shooting or with whatever type of aiming you desire.