I installed Talley 1 piece rings/mounts on 2 of my rifles and had the same issue. 1st set installed on a Rem 700, low mounts, the Magnification ring hit the rear base. This was using a Vortex scope with 30mm tube. Never shot it cause the eye relief was not correct so bought the mediums and installed them. Sighting in was difficult as the factory scope settings were placing impacts way low and right. I have plenty of scope adjustments so it's no big deal...
2nd rifle is a Win 70 in 264 Mag and I had the same issue, impacts low and right. These were not 20MOA rings/mounts but I noticed that both Talley rings/mounts were the same height. The rear receiver mounting height is lower than the front. Hmm, same for the Rem 700. I had to adjust the scope 16.5MOA vertical and 6MOA horizontal to zero at 100 yards...
After some research I installed a 20MOA base from EGW and Burris Signature Zee rings. I centered the reticle in the scope and after a few shots, I adjusted 3.25MOA right, no verticle adjustment needed.
I've already shot the Win 70 past 800 yards. With the Talley 1 piece rings/mounts, about 800 yards is all the turret adjustment I had left after all of the adjusting needed to zero.