Radial profiles of the coupling term in the equatorial plane θ = π/2, at longitude ϕ = 0, for an m = 5-Kelvin mode and for three differential rotations. The parameters are γ = 2, E = 1 × 10⁻⁵, η = 0.18, N_r = 100, and L_max = 100. Inertial frame eigenvalues are λ = −2.968 × 10⁻³ − 7.372i for Ω_η = 2 implying r_cri = 0.435; λ = 1.231 × 10⁻² − 7.591i for Ω_η = 5 implying and r_cri = 0.704. λ = −4.083 × 10⁻² − 7.929i, for Ω_η = 8 implying r_cri = 0.762.