Time delay ratios of image pairs between the NIE and the corresponding SPT-modified model. The model parameters are (θ_c, ϵ) = (0.1 θ_E, 0.15) and the radial stretching is characterized by f₂ = 0.4. The time delay ratios in the quadruple (resp. double) image regime are depicted with triangles (resp. inverted triangles). The red line shows the source position ratios and the color-coding refers to the azimuth angle ∠β. Top panel: even though the dispersion is slightly larger compared to the quadrupole model, normalized by the ratio is still close to 1 in the double image regime and for opposite images in the quadruple image regime. Bottom panel: the time delay ratio dispersion is clearly related to ∠β (see the text for more details). The impact of the SPT on the time delays is also around a few percent, reaching a maximum of around 5% for aparticular combination of non-opposite images of a source located inside B₁.