Largest normalised growth rate σ/β₀ for several configurations, computed with SWAN for equatorial ellipticity β₀ = 0.2. Visualisations in a meridional section using the normalised axes x/a and z/c, with , , and c = 1/(ab). White dashed lines, given by formula (18), show the critical latitudes on which the growth rate is maximum as predicted by (24). For each case, the type of waves involved in parametric mechanism is specified between brackets. Dashed (grey) curves illustrate the domain of existence of ℋ₂ waves at the resonance (in the regime β₀ ≪ 1).