Constant speed prop, forgot to say that. But on my old RV-4, fixed pitch wood prop, you could change the manifold pressure a few inches with no change in RPM.
Don't have a mechanical MP gauge and that would be a wildly inconvenient experiment to try, and could only try it on the ground.
Adding more volume to the line to the sensor would help faster fluctuations that I don't have but would make the lag worse.
Probably won't get to flight test till Tuesday, but... at one point, had fuel pressure problems and changed the pump. Didn't help, changed the sensor. Still have flakey fuel pressure readouts that I ignore, but I am careful to check the electric fuel pump before engine start.
But the engine runs fine...
RV-9A at KSAV (Savannah, GA; dual G3X Touch with autopilot, GTN650, GTX330ES, GDL52 ADSB-In)
Previously RV-4, RV-8, RV-8A, AirCam, Cessna 175
ATP CFII PhD, so I have no excuses when I screw up