On the top set up, black rings, there is a neoprene or similar bushing inside the front ring that fits tight on the scope and is clamped onto by the ring. That allows the scope to move around, essentially a ball joint of sorts in the front ring.
The lower set up, silver rings and a base, the front mount has a narrowed extension ahead of the front mounting point. That narrowed area creates a place where the base bends. The adjustment screws at the rear are moved and the base pivots/bends/deflects at that narrow section so the scope tube is not in a bind.