From the IMV's I've tested (and I'm not saying that this is correct across the board)the less on time the more pressure is deloped, most IMV's default to full pressure when disconnected. The last scope image looks like it's calling for more pressure. I guess it depends on what the ECU requires at that point, if the vehicle is accelerating hard at that point and the pressure is low (the opposite of the original post) then the pwm signal is demanding more pressure (although the FRP volts are not at; but approaching max press). If it's going into limp then I guess the pressure would drop dramatically as the live data is suggesting.
The question is it over pressuring or under? I recently had a problem with rail pressure and if you look at that post; I captured the correlation between FRP volts and PWM signal as the pressure drops off.

Mark