Phase portraits of untruncated, secular averaged Hamiltonian (1) in (Δϖ,e) space, computed in the same conditions as B16, i.e. assuming parameters m′ = 10 M_⊕, a′ = 700 au and e′ = 0.6 for P9. Plots are drawn for various semi-major axis values listed on top of the panels. On each plot, the red curve separates regions where both orbits cross from regions where they do not. In the a = 50 au case, the orbits never cross; for a = 150 au and a = 250 au, the orbits cross in the regions located above the red curves around Δϖ = 180°; for a = 350 au, a = 450 au and a = 550 au, the orbits cross in most configurations, except above the red curves centred around Δϖ = 0° where both orbits remain nested.