it does not "sag", that is the incorrect way to look at it as it implies something is wrong etc.
The rear spring perches are lower on the P5 from what I understand, or also the P5 OEM springs are an extra coil longer; along with differences in the wheel arch position makes the rear look lower than the front.
The front will look about .5" higher than the rear from what I can see. You can be ok with it or you can try to lower the front to match the rear, or get MSP rear struts so that they raise up .5" to match the fronts.
I'm considering using MSP springs and adjusting them for even ride height. If I do it I'll report back.