I think I DID find the answer in my pilot handbook. The range curves
show significant increase in range with the same MP and lower RPM.
Manifold pressure 22" and 1800 RPM for example. In descent the reduced
power would be made up for by gravity for a more constant airspeed. I
think I will try this.

Still like to hear what other people do.

I fly 24 square. when decending I push the stick forward. I watch my airspeed
so not to get to far into the yellow arc. Watch my
MP so that it does not go much above 24.
HANK