This, a hundred times.
P7s are zeroed from the factory using different sized sights. Most aftermarket night sights are made in one size only. If your P7 doesn't match the size of the aftermarket sights, your POA/POI will change, sometimes drastically.
Sent it to Tool Tech, and get the factory sights drilled out. The P7 sights have plastic inserts for the white dots, not paint. Tool Tech will drill out the plastic inserts, and install Trijicon tritium lamps into your factory sights. It's more expensive than the aftermarket sights, but it preserves the factory look, and no risk of POA/POI shift.