I think maybe I've said about a hundred times that the reg controls mid range. If you are constantly running in the mid range, maybe a little richer would help, but it may foul up the transition somewhat. The only thing to do is try it.

My hunch, though, is that you are hovering the airplane in the mid range constantly and not getting enough cooling airflow around the engine. Don't forget that hovering loads the engine very heavily and they will tend to run hotter than they would at full throttle in level flight.

Good Luck!