Yes - I would think a richer mixture would be necessary to
theoretically get to the 96.1% power level with gasahol. That the
mixture has already been optimized for gasoline would make me expect an
even greater power reduction for gasahol. Actually, there are many
things that affect the mixture distribution more in an engine that the
improvement of a mixture shift would be pretty insignificant.

The accuracy of the mixture control and distribution in smaller and
older aircraft is pretty mediocre by any modern EFI standard.