For all systems, only two λ windows were selected for turning on the restraints, but high overlap (> 0.2) was observed for this stage (Figure ). This reflects the fact that the restraint selection algorithm selects restraints which minimally perturb the ligand's native interactions. As expected from the σ ∂H ∂λ plot (Figure ), similar λ schedules were usually generated for the same transformation in the free and bound legs, meaning that reasonable schedules for the bound leg may be determined from the cheaper free leg initial test simulations. However, there were exceptions -for example, more windows were used for the PDE2a free discharge leg than the bound discharge leg due to the greater variance of the gradient observed in the free leg. A detailed breakdown of the sampling time allocations is provided in Section S18. Generally, the compute time was concentrated in the bound discharge and especially the bound vanish stages, and increased with increasing ligand size.