I agree with dschuetz68, You should still have enough adjustment. I would suggest backing out the zero stop allen screw completely. I have a 20 MOA rail on my Ruger Precision Rifle and am zero'ed at 300 yards. I repositioned the zero stop plate ( not recommended because of the VERY SMALL set screws ) so that I could be zero at 300 and come down 7 MOA more .. though I only need to come down 4 MOA for 100 yards. Point being you should be able to zero at 100 even wth the 20 MOA rail.