Ratio of polarized and scattered flux as a function of disk IR excess for debris disks observed with HST/STIS (black markers) and for the HD 129590 disk measured with SPHERE/IRDIS in the H band (orange marker). Green markers indicate model-predicted positions for a disk inclined at 30° with p_max = 0.1 and p_max = 0.2 (for comparison with HD 181327 data point), and a disk inclined at 80° with g = 0.7 and p_max = 0.3 or p_max = 0.4 (for comparison with HD 129590 data point). The axis ratio of each elliptical marker corresponds to the ratio of the minor to major axis of the respective disk, thereby visually representing the disk inclination.