Similar to Fig. 5 but for c_A(0) = 1.2, u₀(0) = 0.8, u₀(L) = 0.2 and λ = 2. In the middle and lower panels, the real and imaginary parts of the eigenmode frequencies are plotted against the length of the intermediate layer L_m where the flow is constant. The upper panel corresponds to L_m = 0.3.