On my MTV-15 on my Lycoming O-360, I find that my best performance is achieved with the engine 2" oversquare. The MT 3 blade props have a greater "activity factor" so a slower RPM can be beneficial.
Interesting, I've been cruising around for the last week trying every MAP/ RPM combo to see where I felt my O-360's cruising "sweet spot" was based on just listening to the engine, general gut feeling and the airspeed, and found that 24" @2200RPM leaned to peak felt just about right, I'm waiting on the replacement for the lost power chart arriving but I'm estimating that setting puts me at no more than 75% power ( or at least I hope they don't)
Also what's "activity factor" ? Do you mean those composite props slap around a bit more than the factory recommended metal Hartzell on the Lyc.360?