I get it. Sometimes good enough is...good enough. It's a hobby so we don't have to be obsessive about the numbers all the time.
Doing it most of the time is sufficient
My example is a .177 bottle gun I use for gray squirrels. Efficiency isn't very good, something like 1.0fpe/ci, but 100 shots is enough to vanquish an entire neighborhood of them so I just leave it be as long as it continues to put the pellet precisely where asked.