Time delay ratios of image pairs between the NISg and the corresponding SPT-modified model associated with the curl-free deflection field . The model parameters are (θ_c, γ_p) = (0.1 θ_E, 0.1) and the radial stretching defining the source positions is characterized by f₂ = 0.4. The time delays are evaluated for pair of images and . Properties of the source positions β^⋆ are shown in Fig. 11. Top panel: Δt^⋆∕Δt normalized by the ratio |β^⋆|∕|β| is close to 1 in the double image regime and for all combination i and j of images θ, in the quadruple image regime, when the azimuth angle ∠β = 0°. As ∠β increases, the time delay ratios Δt^⋆∕Δt deviates from |β^⋆|∕|β| and the corresponding σ(Δt^⋆∕Δt) also increases. Bottom panel: the impact of the SPT on the time delays is around a few percent, reaching around 8% for source positions β located almost on the radial caustic curve.