Orbital eccentricity e versus M₂/M_2,0 for e₀ = 0.6, as computed within the semi-analytical model. Solid (black) line refers to a background gas density scaling with distance as a power law with n = 1, corresponding to the profile of the hydrodynamical simulation. Red (dotted), green (dashed), magenta (long dashed) and blue (dot-dashed) refer to retrograde discs with n = 1.3,2,2.2 and 3, respectively.