Each Monte Carlo simulation was run at 2000 K. 2000 K falls within the range of empirical simulation temperatures commonly used for Monte Carlo simulations of disordered rock salt structures and we expect it to capture experimentally relevant trends in the short range order formation. Each simulation ran for at least 5,000,000 trial steps. Values reported from the Monte Carlo simulations are each averaged over five simulations of each composition presented, with 1000 structures extracted from each Monte Carlo simulation, i.e. each value is averaged over 5000 data points. The crystal-torture package was used to extract percolation statistics from the Monte Carlo simulations .