Cosmic-ray transport parameters of Model A are used, except for the Alfvénic speed V_a set equal to 1 m s⁻¹. In this regime, the numerical result u of Eq. (D.4) is equal to the analytic solution u_loss. The relative difference between u and u_loss is plotted as a function of kinetic energy E_k. The low-energy boundary prescriptions of Table C.1 are respectively featured by the solid red (L1), long dashed orange (L2), short dashed purple (L3) and short dashed-dotted green (L4) curves. The most precise condition is L3 while the worst one is L1.