Target stars’ polarization efficiencies. Colored points (green, blue, and purple for Near Group, ζ Oph Group, and Far Group, respectively) represent individual targets, while black points represent the weighted averages of each distance group. The dashed line is the polarization efficiency limit determined by K. Serkowski et al. (1975), and the dotted line is the limit from G. V. Panopoulou et al. (2019). The dashed–dotted line represents 25% mag⁻¹ as a reference.