I have a friend that has a Mini-14 that has a similar problem. He was trying to sight it in this weekend and he had the scope cranked fully to the right and he was still about an inch short of being on target. He also had it cranked just about all the way up.
When I read your post a thought occurred to me, what if you tried swapping the front and rear ring positions or turning one of the rings 180° and see if the point of aim changes. Then you would know if the problem was in the rings, or you may find a position that works.