I think it was the Rogues list this came up on before ...

Someone did tests through naked, PW/leather, Banded/Bronze. They used
buffs to raise the AC in a lower armor to match thier unbuffed AC in a
higher armor.

So you'd have person with AC X in leather with buffs, and then same
person with same AC X in bronze but unbuffed. This was done with different
AC X's.

The results posted of the most well designed tests indicated that the
protection factors are rolled into the AC. The damage and damage pattern
was the same at AC X, regardless of what armor/spells got you to AC X.
This was true for more than one AC X. Would anyone on this list care to
replicate the tests?

-Lora
Starling Erollisi
Melodie Brell