Comparison between the values computed with the scaling relation estimated in the f(R) strong field scenario, (red triangles), and the ones assuming the reference scaling relation considered in this paper, (black points). The former values are shifted horizontally by 0.1r_⊥/r₅₀₀, for visual purposes. The theoretical f(R) predictions were computed using the M₅₀₀ values obtained from the f(R) scaling relation. The shaded coloured areas show the theoretical uncertainties caused by the fitting uncertainties on the cluster mass distribution, and the dispersion of the cluster redshifts. The vertical error bars represent the range of the parameter containing 68% of the marginalised posterior probability, while the horizontal error bars show the dispersion of the galaxy transverse distances in each given bin.