The 'best economy' and 'best power' means different things in different POHs.
It should probably mean "peak EGT', and approximately 100F ROP which delivers best power at a cost of about 10% worse fuel consumption.
But in the days when most POHs were produced these operating conditions were not as well understood as they are today, and virtually all of them would have been produced simply by reference to engine manufacturers' manuals rather than by having an accurate fuel totaliser in a test aircraft, so you need to take it all with a pinch of salt.