Propagation method results using a constant acceleration a constrained by the observed plasma speeds at the inner and outer spacecraft. All quantities are shown as functions of t_in. The colors in panel a are values of ΔV = ⟨V_p, SolO⟩−V_out, and the black curve shows the radial acceleration for the minimum of |ΔV|. The method results shown in panels b, c, and d all correspond to propagations considering this acceleration. Panel b shows in blue V_in calculated as in Fig. 3, in orange ⟨V_p, SolO⟩ defined as the proton bulk speed measured by Solar Orbiter and averaged for Δt = 1 h centered on t_out, and in green V_out, which is the theoretical speed given by Eq. (8). The corresponding d_min is shown in panel c, and the corresponding τ and t_out are shown in panel d.