NIR extinction of a⁴D J=7/2 lines relative to the 1.644 µm line (horizontal and vertical dashed lines.) Top: Observed (‘o’) and modeled (‘*’) line ratios for all four jet locations in this study. Middle: Difference in extinction relative to the 1.644 µm line. Bottom: Derived β_λ values, normalized by the extinction at 1.644 µm, which is computed as an average over existing NIR extinction curves. This is compared with empirically determined NIR extinction curves, C89 from Cardelli et al. (1989), and the modeled extinction curves, WD1 by Weingartner & Draine (2001) and KP5 by Pontoppidan et al. (2024). We include R_V = 3.1 and R_V = 5.5 for applicable curves to illustrate that NIR extinction in the 1.2–1.8 µm range is largely independent of R_V and shows minimal differences between independent studies. Dashed lines mark the reference line ratio, extinction difference, and β_λ value at 1.644 µm (horizontal) and the wavelength of 1.644 µm (vertical) in all three panels.