A fixed pitch prop is a bit like driving in one gear. The only way to maintain your hypothetical 60% power while reducing rpm is by changing the propeller pitch.
If you pull up and reduce airspeed your rpm would drop, perhaps even down as low as your static rpm speed (usually 2-300rpm) but a propeller doesn't "coast" the way a car can on a flat, at least not in steady level flight.
If 2800rpm at 60% power was uncomfortably high the solution in a fixed pitch situation is to fit a cruise prop, one with a bit more twist.
Static RPM (Powerplant speed on runup) will be lower again, acceleration is slower, (more runway needed). But you would have lower cruise rpm and sometimes a bit more speed. Analogous to driving in a higher gear.
In any event if the POH approves the setting it is fine. The higher/lower engine rpm is one of the compromises that needs to be accepted with a fixed pitch installation.