Notes. Comparing different best-fit lens mass models. For DMH with PIEMD and NFW profiles, the ellipticity is always a free parameter. For the BCG however, there are circular models with axis ratio b/a = 1 (indicated with subscript “cir”) and elliptical models (indicated with subscript “ell”) where b/a is a free parameter. For all the CMs, the profiles are circular. The best-fit χ² is listed in the second column, with corresponding rms offset between the observed and model-predicted image positions as δ_rms in the fifth column. The number of degrees of freedom (d.o.f.) is the difference between the number of constraints n and the number of total free parameters k = k_source + k_lens, where k_source is the number of free parameters for the source positions, and k_lens is the number of free parameters of the lens in each model. In other words, d.o.f. = 3 × 2 × 7 − (2 × 7 + k_lens), given the 7 background source galaxies that are each lensed into 3 multiple images (i.e., n = 3 × 2 × 7 and k_source = 2 × 7). The best-fit log likelihood, log($\widehat{\mathcal{L}}$), BIC and AIC are listed in the last columns.