On average, HetPCM with ε nonp = 4 shows a smaller difference from the experimentally measured pK a values for the flipped acid form (1.16 pK a units) and the HetPCM model using ε nonp = 10 has a smaller difference for the acid form (1.28 pK a units). For the unflipped acid, the homogeneous PCM has a very slightly smaller average difference (1.26 pK a units) as compared to the HetPCM methods. To obtain better agreement with experiment, one might construct a larger QM model of the active site, or else include a larger number of low-energy configurations in the averaging.