Stage 2 engines
On the designs I'm working on, the tendency is to go for the largest upper-stage bell you can get away with, since it improves performance (there's an upper weight limit, of course). I assume the same is true of most designs. The staging clearances, of course, tend to get smaller, never mind the length of nozzle you have to drag out of there.
Some advanced designs get fancy with this, like the RL-10 used on the Delta, which has an extendable nozzle. Helps with length, at least.
Didn't know that about the ring. Thanks!