The reason for the lower variance in the BAR V estimates from model H, compared to model C, can be linked to the differences in the amount of overlap observed between the potential energies of the data and the potential energies of the samples drawn from the models during training (shown in SI figures 2 and 3). When taken together, the current results show that in the large systems containing 64 molecules and at the higher temperature (50 o C) (green error bars in Fig. A and B, ii), both models tend to approach a bottleneck in accuracy.