It must be dependent on the action.
I've mounted the 2.5-20 on a lone peak long action and a bighorn long action. Each had about 3/16" to play with, not much room but doable. Both those rifles have Hawkins rings if that helps.
Yes initial impressions are very good. I will be mounting it this weekend. Glass is very clear, I like the reticle and it's a great size for what I like.