Upper panel shows the mass profile of the original NIS lens (solid curve), and that of three SPT-transformed lenses, with parameters f₂ and γ_p indicated by the labels. For all of these three models, Δα_max ≈ ε_acc = 5 × 10^-3θ_E. Since the transformed mass distributions have a finite ellipticity, the density is plotted as a function of the geometric mean of the major and minor semi-axis of the best-fitting ellipse to an isodensity contour, except for the case with negative f₂, for which the outer isodensity contours are not closing around the lens center; in this special case, the x-axis corresponds to the θ₁-axis. The convergence changes up to 28% for radii smaller than 1 θ_E, radii larger than that show a significantly smaller convergence for a positive f₂. Negative f₂ show an essentially mirrored behavior compared to positive f₂. This leads to convergence that may not decrease monotonically. The lower panel shows the ratio between transformed and original mass profile.