You're right, the AI heroes have one PoI (already used one potion or the spell with similar effect) "on" right there from the very beginning of a battle when playing the game on the highest two levels of difficulty. But the problem is that no matter how many PoI's the mapmaker gives them, the AI just don't know how to use the potion. It will just toss them aside. It won't use them simply because, quite frankly, it seems to lack the ability to do so. It would be nice to "extend" the effect for the AI or then painfully try to teach him how to use PoI's. I guess the latter option would require extensive digging and searching the code. The Equilibris team has to do things without Ubi's assistance so it's another Long and Winding Road ahead...
Yes, I recall the majority of people visiting this particular forum being against the idea. I'm glad I'm still in one piece after my "most grievous sin", talking without knowing the hard Heroes IV facts. Well, same place, same time next year, eh?
Don't worry if things are going badly today. They will be much worse tomorrow.