The low speed is as lean as it will go while still being responsive. I spent quite a bit of time carefully tuning the engine so it is as responsive as possible, I know what you mean though, intially leaning out the low end a little resulted in a pick-up in idle rpm and a slightly smoother idle.
The plug is new and the engine is pretty well broken in now, so I am at a loss as to why it is determined to idle so high.