Radial dependence of Γ_rad (red, solid line, upper panel) for our supergiant test model, plotted over the Rosseland optical depth τ_Ross. The mean value obtained with Eq. (29) is indicated as a dashed-dotted line. For comparison, Γ_e and the total continuum contribution Γ_cont are also shown. Lower panel: difference between g_grav and g_eff is illustrated: the red solid curve marks the actual difference at each optical depth, while the dashed-dotted line denotes the difference using . The gray dashed vertical line denotes the location of the sonic point.