Variation in log₁₀(W₈₆₂₁/A_V) as a function of log₁₀(A_V) for each target cloud. The corresponding A_V scale is shown at the top of each panel. The points are color-coded by their number density, estimated via a Gaussian KDE. The blue squares represent the median log₁₀(W₈₆₂₁/A_V) in bins of log₁₀(A_V) (from −0.8 to 0.6 with a step of 0.1). The solid red line and shaded region show the selected PLM and its 99.7% credible interval, respectively. The vertical dashed orange lines indicate the knot locations (see Sect. 3.1). The full PLM fitting results with n_p = 1−4 for each cloud can be found in Fig. B.1. For Cepheus South, the points marked with black crosses were clipped as outliers and excluded from the fit (see Sect. 4 for details). Each panel is labeled with the cloud name, distance, and the number of sightlines.