If you go over 200 AIP, then the reinforcements stop increasing, and the extra strength goes first to the strategic reserve, then to waves and the next CPA.
I hate AI War for being so cryptic around things like that.
That's one thing the game definitely needs to do, is be less cryptic. About everything.
Hell, that can be a really frustrating reason to lose, is because the game does something like, I dunno, give you a message, which is important, but you have no bloody clue what it means. One early loss I had was to a Champ Nemesis wave.... the message popped up, and I had no freaking clue what the heck it even meant. And of course it doesn't list a planet for something like that, so I don't know WHERE it's going to go.
Countdown hits zero, I'm watching the galaxy map to see what's happening.... nothing happens for awhile... and then ZOOM, those bloody things and their stupid shields are on top of my home system before I could do anything. That game ended there. If I'd had a clue what the whole thing was, I mighta been able to do something about it (I have a pretty specific response to that event now). But nope. And the game does tend to do that.
Or something like a cross-planet attack. The player has no bloody clue what that means when they see it the first time, and when the countdown hits zero, it then gives you a couple of other messages that also wont make sense. There's no way for them to know what happens there. It's not like the "incoming wave" message, which is very clear about what's happening.
Hell, I still don't entirely understand CPAs myself. There's just no real info on them in the game (and the wiki is mostly useless).