Top left: as a function of R_o and Λ_E for non-axisymmetric retrograde waves (m = 1). Middle left: same for corresponding prograde waves (m =  −1). First, the left-top white corner region for which R_o ≤ m²/2   Λ_E corresponds to the domain where and where the waves are thus completely vertically trapped. Then, the region where corresponds to the regime where the MHD TA applies (i.e. |ν_M;m| < 1 and ) and where the vertical trapping is weak (i.e. m²/2   Λ_E ≪ R_o). Next, the domain where is weak corresponds to the regime where the MHD TA does not apply (i.e. |ν_M;m| ≥ 1 and and thus θ_c;m ≠ 0) and where a partial vertical trapping operates. Bottom left: net bias between retro- and prograde waves evaluated through (for m = 1). This is in favour of retrograde waves since as emphasised in Sect. 2.4.3. prograde waves are more trapped in an equatorial belt than retrograde ones, the vertical trapping being independent of the sign of m. Right: same for m = 2 and m =  −2.