Relative error on the average surface mass density Σ(< R) as a function of radius from the BCG for the best-fit models of Mock mass distribution 2. From top to bottom: single plane cluster, cluster (without LOS perturbers) from multi-plane models, and total multi-plane configuration. In each plot, the lines represent the input (solid black), the multi-plane model (dashed magenta), the single-plane model (dashed black) the model where we assumed constant mass-to-light ratio (light blue), the model where we assumed spherical galaxies (red) and, only in the multi-plane cases, the model where we assumed only spherical cluster members (blue). We note that in the total multi-plane configuration the Σ_Eff is derived from the total deflection angle and computed for a source at z_s = 2, as explained in Sect. 2.1. We observe that at θ_E,tot ~ 10^″ all models converge to a certain value of Σ(< R) and Σ_Eff in the top and bottom panels, showing that strong lensing provides accurate mass enclosed within the Einstein radius.