except...
the preceding is valid so long at the blade angle has not reached the fine pitch stop. If your power setting was low to start with, thew blade angle would be fine, and when it reached the fine pitch stop, any reduction in airspeed will result in a reduction in RPM.
When operating at a high angle of attack, the inflow to the propellor is not axial, but is oblique to the axis of rotation. At such times, the descending blade, RH on the PA-34 from aft for the left engine, opposite for the RH engine, has a higher angle of attack and also a higher inflow velocity than the LH blade. This causes an asymmetry of lift, being offset from the center of rotation, which increases some vibration, and results in the P factor issue on non CR aircraft.
The governor is balancing the total drag force of the blades which is dependent on the sum of each blades drag, which are different when any inflow is not axially aligned with the propellor, with the torque being output to the propellor hub by the engine. Within the governing range of blade pitch. Outside this range, RPM will vary.
regards