RPMs incorrect from percent, but all else is spot on

Using the modern prop model on a 172 realism project, I have perfected the thrust, % power, and airspeed to match the POH perfectly at multiple altitudes. The engine is modeled after an exact true aircraft engine (friction and power) and performs perfectly.

My issue is, that the % power is about 200-400 rpm off from book value and I can not seem to get the identical performance while raising RPM, it throws this or that somewhere in the curve out.

I need some outside ideas to reconfigure this to get the RPMs up but all else remains the same, literally need a scalar for RPM, I thought about just using the gearbox ratio as that is almost exactly what is needed, but then I know I just kicked the realism out, and the static RPM would be thrown off at the same time.

Have reconfigured the prop multiple times, but it always ends up throwing some other item off. RPM could be on with % power, but the thrust will be off, it’s just never ending.