Plots of $\overline{Q}/\overline{I}$ (left panel) and $\overline{U}/\overline{I}$ (right panel) as function of B. The results are obtained by performing PRD–AD calculations for three LOSs with μ = 0.1, 0.6, and 0.9 (solid, dashed, and dash-dotted lines, respectively), χ = 0, and considering uniform horizontal (θ_B = π/2 and χ_B = 0) magnetic fields of different amplitudes. Blue, red, yellow, and purple lines correspond to profiles obtained with the FAL-A, FAL-C, FAL-F, and FAL-P atmospheric model, respectively.