Are the flavor/aroma compounds in a single variety of hops proportional to the AA%? I don't think so, but thought I'd open it up for input.
This is an arbitrary example:
Assume a recipe which calls for 1 oz 4% Saaz 20 min and 1 oz 4% Saaz at 10 min. The Saaz available is 2% AA.
If I adjust the adds strictly for IBU contribution to the beer, I'd need to use 2 oz for each add. In this case, it seems that flavor contribution may be greater than expected.
If flavor contribution is independent of AA%, then I'd stick with the 1 oz adds and adjust for IBU with the 60 min bittering add.
This would only be an issue with low alpha hops with a wide AA% range.