Best power vs best economy
Let's say the POH power setting tables say 65% power is 2,400 RPM. When leaning to best power or best economy, is it assumed that one ensures RPM remains at 2,400 after leaning? If so, why does one get lower airspeed when leaned to best economy? If not, what RPM are you supposed to set then?
What I have in mind is small piston engines with fixed propellers, but I suppose similar principle applies to heavier stuff.