Distributions of the best (successful) macromodel parameters, s, q, ϕ_q, γ, and ϕ_γ − ϕ_q, for three kinds of perturbations (m3, m4, m3+m4), each added to EPL+γ to fit both image positions and flux ratios (assuming σ_f = 2% and σ_p = 10 mas, essentially the last row in Table 4). The vertical lines indicate the parameter values of one example successful mass model from m3+m4+PAv+Qv, for which the image configuration along with the corresponding critical curves and caustics are shown in Figure 13.