Slope, value of best fit line at M_V =  −20 and scatter of the median RS values of the 100 Monte Carlo runs for each cluster versus cluster velocity dispersion (σ_clus, left panels) and cluster X-ray luminosity (L_X, right panels). Error bars refer to the error of the median of the 100 simulations. In red (on-line version), clusters whose RS is contaminated by another structure (see text).