1.18 would fit with ease, but definitely do go for the direct mount to the receiver dovetail if you can.
I have an Impact Precision with the 20 MOA rail, the SP-4601 with an extra 20 MOA and 1.18" height, and a heavy varmint barrel contour to boot. The objective lens housing on my PMII still has enough room that there's a gap of 0.1-0.15" between the bottom of the standard Butler Creek caps and the top of the barrel.
I wouldn't be able to fit all that much lower, not that they make any that are lower, but even with 40 MOA of inclination and a heavy varmint contour the 1.18" was plenty.