Left: radiative acceleration normalised to gravity. Right: effective temperature (solid) and electron temperature (dashed) stratification for specific models from Fig. 1. The grey horizontal line in the left panel is the radiative Eddington limit, Γ_rad = 1. The inset plot in the left panel shows the zoom-in of the sub-critical region. The grey vertical line in the right panel is marked at τ_Ross = 2/3. In both panels, the black solid line represents the base model, while the coloured solid lines indicate models where each of the following parameter is varied from the ‘base model’: L (red), M (blue), X (magenta), and Z (green).