Contour plot of effective to mean opacity ratio, χ_eff/⟨ χ⟩, for complete background opacities (i.e., sum of background lines + total continuum, see text), displayed as function of radius (abscissa) r/R_* = 1 − 100 and the full considered wavelength range (ordinate) between 5 and 10⁷ Å. Colors range between no opacity-reduction 1 (white) and the limiting value f_ic = 0.01 (black). Parameters according to ζ Pup like model thick1 in Table 1.