The high mount uses a different base that is on a different angle to center the scope over the receiver. I can't seem to take pictures small enough to post on this platform if I could I would be able to show you the difference.
The number 1 base is for your receiver and low ring set.
The letter U base is for your receiver and the high ring set.
If you look at a U base next to a 1 base the U base looks like it was shaved on the inside and made narrower at the bottom canting to the left to get the ring set centered. That's your problem the wrong ring set on the wrong base. You need to look at the base see what is stamped in it and get the matching ring set.
