I've flown Fast Combat for over 20 years and know the difference between a lean run and an engine that is using too much nitro or is overcompressed. An overcompressed engine will trigger lean runs because that is what they do, they COMPLETELY burn the mix and THEN SOME. During the middle of a real good run, you can hear the plug "go away" and the diesel action takes over from there, with just a slight drop in rpm. Decrease the compression [or the nitro] and the tendency for the mixture to end up too lean decreases.
There are many more reasons for a run to get too lean, but no one has ever hurt an engine by lowering the compression a little to see what happens.
I would not run a high rpm piped engine without a hand full of different thickness shims and a variety of props to solve the blown plug issue. This assumes that all the other basic "engine hygene" issues are already met.