At what point do you call a riv bet HU w. A high?

[Fryguy]

Weird paradox:
The bigger the pot, the more correct it is to call with A-high mathematically. However, the bigger the pot, the worse the chances are that A-high wins because people are obviously interested in their hands.

There's a balance point somewhere, just not sure where it is. I almost never call down with A-high in fullring games. It happens a bit more often in 6-max.