Are you using the mounts that are split vertically?
I managed to shim between the rail and the mount with a piece of pellet tin lid, it's only 0.22mm thick, and the declination of the rail is around six times that, so it doesn't go very far to correct the problem.
I have to say, although it doesn't do the job I'd like it to, the little shim does clamp down well and make a very firm mounting for the scope.
The combination of the AR20 and the T35 is very impressive. I used mine for 20 yard bench rest last Friday and the first card I shot was a personal best.