Posterior distributions for some analytical model parameters (smooth potential and smooth source), based on parameter covariance matrices computed either from the FIM or via HMC sampling (see Sect. 2.6). The three colors correspond to the three mocks of Fig. 3: localized subhalo (LS), popluation of subhalos (PS) and high-order moments (HM). Dot-dashed distributions in the upper right triangle correspond to fully smooth models, while distributions in the lower left triangle correspond to models including a pixelated component to account for perturbations of the smooth potential. Parameters are, from left to right: Einstein radius of the lens θ_E, ellipticity of the smooth lens potential {e_1, ψ, e_2, ψ}, external shear components {γ_1, ext, γ_2, ext}, central intensity of the source I_Sersic, half-light radius r_eff, Sérsic index of the source n_Sersic, ellipticity of the source {e_1, s, e_2, s}, position of the source {x_s, y_s}. Overall, parameter biases are reduced after including a pixelated component in the potential to model deviations from smoothness; however, some still remain, in particular for lens LS, for which turning to an analytical model informed by the pixelated model is warranted.