Numerical solutions of the deflection test set-up when assuming a differential cross section Eq. (4) that is peaked at a single value of the deflection angle, given by θ₀ = 0.2 here. Both panels show the angular distribution function f(t, θ)⋅sin(θ) at various (early) times t, for σ_T/m_χ = 100(10) cm² g⁻¹ on the left (right) side. In both cases, the simulation result agrees with the Gaussian Molière approximation Eq. (27) only after some minimal time t > t_min(θ₀). This minimal time is shown in Fig. A.3 in the main text, and compared to the theoretical expectation, finding good agreement.