Derived MIR extinction from [Fe II] lines (λ > 5 µm) tracing different excitation conditions compared to NIR [Fe II] lines. The plots show MIR extinction, where MIR [Fe II] lines trace different excitation conditions (n_e, T_e) than NIR [Fe II] lines. Top: β_λ values assuming MIR line intensities correspond to gas at half the NIR-traced temperature (f_T = 0.5) with the same electron density ($f_{n_e}=1$). Middle: same temperature as NIR-traced gas (ƒ_T = 1.0), but assuming MIR lines trace half the electron density ($f_{n_e}=0.5$). Bottom: both temperature and electron density are halved (ƒ_T = 0.5, $f_{n_e}=0.5$).