Phase portraits of secular averaged Hamiltonian for different values of the perturber’s eccentricity e′ and a fixed semi-major axis ratio a/a′ = 1.2, as a function of the longitude of periastron of the particle relative to that of the perturber ν = ϖ − ϖ′. The red curves separate region where the orbits actually cross from regions where they do not. In the case e′ = 0.1 (left), the orbits do not cross below the red curve, while for e′ = 0.5 and e′ = 0.94, they do not cross inside the curves around ν = 0.