If the length is the problem, the ProStaff that came on one of my 111's had an extended front base.

I'd use this as an excuse to get some Leupold rings and bases on there, and incidentally, that's what I'm doing. I've got a set of Leupold DD rings/bases showing up Monday for the 111/ProStaff setup. I'll let you know how it goes, the Axis and 111 round receiver uses the same mount.