Left panel: the dashed line represents the P amplitude fit to the center-to-limb THEMIS and IRSOL measurements from Paper I. Calculations with a constant anisotropy factor f cannot reproduce these amplitudes (asterisks for f = 5 and triangles for f = 0). The right panel shows the corresponding height dependence of f (dash-dotted line for f = 5 and dotted line for f = 0). It was varied linearly (solid line, right panel), which created a good fit to the measured P amplitudes (diamonds, left panel).