To build a collection of representative RBFE perturbations, data was drawn from all publicly available FEP benchmarking series (n=18) as defined in recent work from the Open Force Field Initiative and Merck. Within each series, all possible pairs of ligands were picked. Next, perturbations that involved ten or more heavy atoms perturbed or a change in formal charge were discarded (as these were deemed likely to be highly unreliable with the chosen RBFE protocol).