your objective lens is 42mm but your objective bell is 50mm. 50mm divided by 2 is 25mm, 25mm is .984" add in the 20moa can't from you base (if you have it) and you are an inch. thus the lowest you can go is going to be just over an inch. add in enough height for your lens caps if you run them. 1.125 should be good.
if you did not have an AX with the full top rail you could go lower.