Minimal timescale t_min(θ_c) after which the hSIDM approach is applicable (extracted from the deflection test set-up). The symbols are derived from a comparison of numerical solutions using the hSIDM scheme with the result obtained when using the numerically expensive explicit sampling technique for all scattering angles (anisotropic rSIDM scheme). We show results for θ_c = 0.1, 0.3, 0.5, 0.7, 0.9, and for differential cross sections with anisotropy parameter r = 10², 10³, 10⁴, respectively. We furthermore consider the case without recoil and with ‘Rutherford’ scattering cross section (upper panel) as well we the case with recoil and with ‘Møller’ cross section (lower panel). Solid lines show the dependence of the analytical prediction Eq. (35) for t_min(θ_c) on θ_c and on r.