(a) Dependence of the amplitude H_HeII on the average temperature log T_HeII in the HeII zone. The input physics and label are the same as in Fig. 5 for models of mass 1 M_⊙ and solar metallicity. Dotted lines show the log T_HeII − H_HeII coordinates of the RGB and AGB models presented in the right panel. (b) Γ₁ profiles on the RGB and AGB roughly at a similar Δν = 1.03 μHz. The arrows indicate the amplitude and the width of the Γ₁ variation at the helium-second ionisation zone, in blue on the RGB and red on the AGB. (c) Same as panel a, but with the average density log ρ_HeII in the HeII zone instead of log T_HeII. (d) Logarithmic differences between the AGB and RGB models shown in (b) of the temperature (dot-dashed red line) and density (dashed green line) as a function of the normalised acoustic radius. The vertical solid and dashed lines indicate the location of the base of the convective envelope in the RGB and AGB models, respectively.