PP is based off of direct damage, with a little fudging for DoT damage. Basically, if you take a look at the top spots in any raid, you can see the PP ratios, and they hold true no matter who does it, though it does vary based on the actual battle level. For example:

The PP ratio for an Expert match is about 0.008 pp per damage. So if you do 1 Million damage, you'll have about 8,000 PP. It varies between .0081 and .0079.
I forget the exact ratio for standard matches, but it's significantly lower, like maybe a third of that? It's been a long time since I actively farmed those.
Ragnarok gives you the best ratio, at about 0.02 - so nearly 2.5x more than Expert. Do a million damage on a ragnarok, expect about 20k PP.

That being said, the above advice holds true - while PP is great and all, aim for getting MVP and ticket production more than anything else. While PP sounds cool, especially getting that sweet sweet 'free' copy at 4 million PP, the time spent isn't really cost efficient. Whereas getting 150 and 150 of the souls gives you useful stuff, the last... 2 million PP give you absolute junk comparatively. From 3-4 is obviously lacking, but even before then the rewards are few and far between. Take a look at the reward table, you'll see what i mean.

TL;DR. Don't focus on PP - get what you can. Focus on MVP and being able to auto the battles. Kamihime is a remarkably time-intensive game, so anything you can do mindlessly is better.