Howzit Chris,
I too shoot this way. I have chipmunk cheeks and find that if my thumb is up, the arrow aligns better with the eye. I shoot three under and find that "for me" it is more consistant. I don't sight down the shaft but think that subconciouly I gap. When it feels right, arrow is set loose.
Sometimes I get strange looks from other archers on my form/anchor but I figga what da hell, it works so I'll stay with it.
Aloha,
Mark