I think Jim may have hit it on the head. I just gave it a try, and while my sighting line wouldn't have jumped up quite that much, a variation in facial structure and anchor points could make the difference.
are you saying that one would change your anchor point throughout your shooting or be 3 under for all of it?
No, I think he's saying that when the person was shooting out in the field, hunting, 3-D, whatever, he used the same anchor up on his face, corner of the mouth or even higher; and he used that same anchor for all his shooting in the field. However, when he stepped inside to compete in a Vegas, multi color round, or blue face round, he went to a FITA style anchor under his chin/jaw. With this anchor the string nearly bisects the face and chin, and is used to align the arrow with the spot and control left/right alignment. The whole idea is to get as much consistency as possible because the distance never changes, nor does the size of the spot. Hope that helps clear it up??