The left panel presents the distributions of the radial difference Δq_{2−6 kpc} ≡ q_{6 kpc} − q_{2 kpc} for both the successful and failed cases when adopting EPL+γ in the presence of perturbation Qv alone (assuming σ_f = 10%, σ_p = 10 mas), and in the right panel are the distributions for Δϕ_{q, 2−6 kpc} ≡ ϕ_{q, 6 kpc} − ϕ_{q, 2 kpc} when adding perturbation PAv alone. The samples essentially correspond to the fourth row in Table 4.