[Ar VI]/[Mg IV] vs. [Mg IV]/Hu-12 predicted by AGN (left) and shock (right) models. For the shock models we only consider the flux of the broad component of Hu-12 estimated from the broad to narrow flux ratio of Pf-γ. Left: Reference AGN models (Z_⊙ and n_H = 10³ cm⁻³) for the low (blue), mid (orange), and high (red) Eddington ratio SEDs. The shaded areas highlight the range of ratios predicted varying the metallicities (0.4–2 Z_⊙) and n_H (10²–10⁵ cm⁻³). Models with the same ionization parameter, U, are connected by dashed lines. Right: Reference shock models (ram pressure R = 10⁶) for the 0.5 Z_⊙ (green), Z_⊙ (black), and 2 Z_⊙ (purple) metallicities. The shaded areas highlight the range of ratios predicted varying R (10⁴–10⁸). Models with the same shock velocity, v_s, are connected by dashed lines. The observed ratios use the same symbols as in Fig. 3. The models are described in Sect. 4 and Appendix D.