Top panel: ΔN_1,tot (solid lines) as a function of the G₀∕n_H ratio for v_IF = 0.1 km s⁻¹ and for Z′ = 0.01 (blue), Z′ = 0.1 (red), and Z′ = 1 (black). The static N_1,tot are the dashed lines. Middle panel: ΔN_1,tot between static and advection cases as a function of v_IF. The points were obtained for a strong field of G₀∕n_H = 10² cm³. The black lines are the analytical formula presented in Eq. (19). Bottom panel: Same as middle panel but for a weak field of G₀∕n_H = 10⁻⁵ cm³. In this limit, Eq. (19) is a fit made on all the points.