In general, the power level of a voice signal displayed on the P3 will be less than the average power. The reason is that each display point on the P3 is only showing a portion of the total power.

You would see a similar effect on the K3 or other receiver if you monitored an SSB signal with a narrow CW filter. The S meter would read lower since only a portion of the signal is within the passband.

If an AM signal is modulated with a single-tone sine wave at 100% modulation, then each sideband will be -6 dB from the carrier, and it will show that way on the P3. But with voice modulation it will be much lower, both because of the effect I just mentioned and because the average modulation is less than the peak.

Alan N1AL