Left panel: Statistical test values for different subsets, normalised using bootstrapping to allow direct comparison. The grey shaded region shows the 1σ region expected from a uniform distribution. Right panel: Statistical significance of the results compared to uniform simulations. The subsets include the complete sample, BCG ellipticity thresholds (ell > 0.1, 0.2, 0.3), BCG median distance from the cluster centre (R), BCG absolute magnitude relative to the complete sample median in the r band (BCG Mr), BCG colours g_auto-r_auto relative to the median (BCG gr), and the satellite galaxy colour (blue or red gal). The dotted black line indicates the 1σ region.