BAYESLENS marginalized posterior distributions on the free parameters of the Cluster-1 mocks. The contours limit the 1σ, 2σ, and 3σ regions. The black dashed vertical lines in the histograms correspond to the 16th, 50th, and 84th percentiles of the marginalized distributions (these values are reported in the titles). The solid red lines are the true values of the parameters of the mock cluster. Panel a: scaling relation hyperparameters. In this plot, is omitted because its value is not optimized in BAYESLENS, but is directly derived from Eq. (5) assuming γ = 2. Panel b: posterior distributions for the cluster-scale halo parameters, while panel c: average velocity dispersions within apertures of radius R = 0.8″ of the four brightest measured galaxies (BCG, Gal(1), Gal(2), and Gal(3)). Panel d: average velocity dispersions within apertures of radius R = 0.8″ of the three brightest galaxies without a measured σ: Gal(4), Gal(5), and Gal(6). In the plot, the galaxy Gal(7) forming a galaxy-scale strong lensing system (see text) is included. Panels c and d: blue vertical lines indicate the stellar, aperture-averaged, velocity dispersion of cluster members predicted by the best-fit σ^gal − m_F160W scaling relation (zero-scatter solution).