Scatter plots of cluster-halo parameters (c₂₀₀ and M_tot) versus parameters of the modelling of either the BCG or the perturber galaxy n.1 (hereafter P1, see text for details). Here we show the posterior probability distributions obtained in a representative case (case 1 in Table 5). The plotted parameters are: 1. the NFW concentration parameter c₂₀₀ versus the BCG fiducial central velocity dispersion σ_0,BCG (top left panel); 2. the cluster halo mass M_tot versus σ_0,BCGtop right panel); 3. the NFW concentration parameter c₂₀₀ versus the fiducial central velocity dispersion σ_0,P1 of the galaxy P1 (bottom left panel); 4.  the cluster halo mass M_tot versus σ_0,P1 (bottom right panel). The contours show the 68%, 95% and 99% confidence levels. The colour code refers to the value of the χ² estimator.