OK, I am lost. if Charles - 6 corps and Nappy - 6 corps fight a battle, and Charles commands 1 Prussian corps:
In the old game Prussia would, if they won, gain 3PP +1 for Nappy, loose 1 and an aditional -1. I had always assumed the same here, as why the heck would you have a reason to change that? (EiH "enhncement")
So, Am I missing something, what is the current system?
I'm not entirely sure whether the EiANW system is the same in the case you mention as the EiA system (I think there was some discussion of this in another thread, but I don't remember what the upshot was). But you're talking about a case in which both allies actually have corps in the battle. Both in that case should gain/lose PPs (though how many I believe was the subject of disagreement).
The case we were discussing here, though, is a little different, and applies only to EiANW because of the lend-unit system.
In EiA, you just combined movement, and you could supply your ally's corps but they were still his corps. In EiANW, we have lending instead. This means if, for instance, Prussian corps are moving through Austria, they will probably be lent to Austria just for purposes of supply.
Now, if a stack of 6 Prussian corps lent to Austria (with NO Austrian corps present) fights a French stack, the PP gain/loss SHOULD be all Prussia's even though they are under Austrian control and supply. But currently the game would dock Prussia 3PPs for losing the battle AND Austria 3 PPs.