I just called AoA and talked to a sales manager. He told me that I'm shooting too close and the pellet is still traveling upwards. I need to not shoot so close. LOL
There might be some truth to that if you were shooting at 15 feet instead of 15 yards. But it wouldn't account for 5" with your scope height.
Is there a chance that the one piece mount has some MOA tilt to it? I believe most of the ones that do are set up to have the offset/cantilever facing backwards.
I believe you said you reversed the adapter. Might as well trying to reverse the mount although I'm guessing it won't solve your problem.
Someone else said to try the adjustable rings to get the scope lower. I believe the Burris XTR Signature have lower options than the Sportsmatch. Not sure what their dovetail options are.
Are you happy with the height as is? If you bring the rifle to you cheek with your eyes closed and then open your shooting eye are you lined up?