what makes the range longer in the p3p over the p3 4k? is it the controller? or would I have to mod the drone and the controller?

Different and incompatible radio technologies. The P3 4k is essentially a P3S with a 4k camera using wifi formats for signalling, which is a network orientated protocol. Not specifically designed for streaming video. Whereas the P3A & P3P use 'light bridge' which is a DJI Format and works over much greater range. This protocol appears to be optimised for streaming video.
You may be able to add range extenders to boost your current setup. I'm sure you will get some replies from those using such a setup.

so yeah, not something easy

Easy thing to try is turn off the maximum range. Right now the most you can get is 500 meters, right? If your turn that off you can go further, providing you have no large obstructions. I have gone near 600 meter till I ran out of clear space and didn't dare go further. I have a P3S.

Jake Phantom 3  Posted at 2016-11-4 14:08
Easy thing to try is turn off the maximum range. Right now the most you can get is 500 meters, right ...

I didn't see a way to turn that off. I will look later though.