Slight hijack. Most (but not all) action tops are curved to some degree. Most bases are curved to match (ideally a bit smaller radius of curvature so the bases do not touch only on a line between the screws, but on the outside edges.) When you put two surfaces like that together they tend to have a single "best fit" orientation. (I'm simplifying a bit, but not much.) Even if one can get the rings to line up while tightening the base screws with the rings on the bases and held in alignment, this has never seemed to me to be a very robust or stable arrangement. But perhaps it works well enough most of the time.
