Hey Joe,
I think you are right, despite the engine, if the thing will not idle at a consistant speed, then it will slow down and die. Kind of like standing on a wet log. If you are not in the center, things aren't going to get better, you will fall off one of the sides. Also, with the idle mixture being tuned well will lead you being able to lower your idle speed and theoretically slow down your approach speeds at the same time.

I have this problem with my floater planes, they idle just a bit too high and their descent rate is way too shallow, makes for a long landing approach.
Curtis