Evolution of the coupling factor as a function the ratio 2πν/𝒩_b (solid lines), such as predicted in Sect. 4.3 and for different values of α_b = 𝒮_b/𝒩_b, where 𝒩_b and 𝒮_b are the values of the modified Brunt–Väisälä and Lamb frequencies just below the base of the convective region. When considering ν ≈ ν_max, stellar evolution goes from the right to the left. The black dashed line indicates the beginning of the Type-b regime. The dash-dotted lines delimit the end of the Type-a regime for the considered values of α_b, with the corresponding colors.