If your arrow shelf is flat, then an elevated rest, or a feather rest would probably help. Most barebow shooters like to have the arrow as close to their hand as possible, though, as it won't be as sensitive to variations in the cant of the bow, and is more natural to aim.
When I anchor, I have my thumb along the back edge of my jawbone. The other anchor point that I use (it is good to have two or three that you feel each time you draw) is not so rock-steady, as I use the corner of the rear edge of my fletch on my face to feel when I am at full draw. Going from shields to parabolic is not so difficult, but bare-shaft testing is an adventure!
A mouth corner can move, as can a lower jaw, so a lot of good shooters advise touching a tooth in your upper jaw, as that won't be wandering around the range.
Killdeer