Distribution of measurements of ℜ_⋆, marginalising over the distribution of ${⟨{\overline{\rho }}_{2h\star }^{\star }⟩}_{{\mathfrak{R}}_{\star }}$ (minimum in the moving average of the mean stellar mass densities profiles) using methods [i] (left panel) with Eq. (19) and [ii] (right panel) with Eq. (20). The top four rows of panels show the results for the observed systems (Fornax, Virgo, MW, and M31), and the bottom row panels present the simulated TNG50 Fornax-type cluster, with ℜ_⋆ measured in projection (2D) and in 3D.