Reduced vertical radiative flux as a function of the vertical coordinate. We show that in the far upper regions of the disc atmosphere our code reaches the correct flux values. The computed vertically integrated τ = 1 transitions at three different positions in the disc are marked with triangles. The end points of the curves correspond to the 7° angle of our simulations at those disc positions. Compared to the analytical |F_rad|∕cE_rad ~ 0.55 at τ = 1 (Eq. (82.15) in Mihalas & Mihalas 1984) It is evident that our method locates the optically thin–thick transition further inward than the analytical value. This leads to higher temperatures on the τ = 1 surface and thus to an overestimate of L.