Sorry about that WC, my thought was 11mm is about .433 inches. I was way off from 12.5mm, but thinking in terms of .445 inches. My guess is that tip-off rings will take you in the wrong direction, they'd be for a narrower dovetail. There is such a thing as scope rings for 12mm and 13mm dovetails.

Try searching XXmm dovetail scope rings, then view images of the search results for drawings of the dovetail that the clamp part of the ring is intended to fit.