Particle energy spectrum in the plasma rest frame for escaping particle populations upstream and downstream of the shock for different minimum mean free paths at the shock. The box size used in the simulations corresponds to the injected particles’ diffusion length, L_box ( = λ₁v_injcos²θ_Bn, 1/(3u_x, 1) ≈ 3.5 ⋅ 10⁵d_i), upstream and downstream of the shock along the magnetic field line.