It's mounted on a KRAM mount, both to give a little height and more importantly, to move the optic farther back. The KRAM isn't compatible with a BUIS, even a KAC sight. That's a Colt lower, so it's only a 4-position extension, and it's on the 3rd position. When I shoot that gun closer up with the RMR, I push the stock all the way out for my simian arms.

I have a love/hate relationship with the ACOG. Clear, light-weight, and easy to mount a RMR on top. But the eye-relief sucks when doing anything other than shooting in the perfect position. Still, that gun has gone out to 500y in that configuration with Federal M193 on B/C steel, so it's not all bad....unless there's wind.