An ace is an individual achievement and I see no reason why you should be forced to split it with someone else.
If partner A parks the hole then you have a green light to run the chains (which normally would result in a difficult 2nd shot if you miss). IMO, having a risk-free run at the chains is an advantage that you gained by having a partner. Also, with a good partner on an easy course (say like Orchard Park) you can take more risks.
Having said that, I think there is a difference between a $50 Orchard ace pot and a $500 ace pot. For larger amounts, I would talk about it before hand (80/20 split, etc.). I view getting any cash from a partner's Ace as a thank-you... not an expectation.