Angular distribution f(t, θ)⋅sin(θ) of beam particles within the deflection test set-up as obtained within the hSIDM scheme at three (very early) times t (solid lines) and for two values of the critical angle, θ_c = 0.3 (left panel) and θ_c = 0.5 (right panel), respectively. The angular distribution is expected to agree with the analytical result Eq. (18) (dashed lines) after some minimal time t > t_min(θ_c) for which scatterings by angles θ < θ_c are sufficiently frequent such that the effective drag force and momentum diffusion approach applies. The agreement is indeed reached after the expected time t_min(0.3)≃2 ⋅ 10⁻²t₁ and t_min(0.5)≃4 ⋅ 10⁻²t₁, respectively. We note that hSIDM is thus well applicable on the relevant dynamical timescale t ∼ t_dyn(≡t₁).