Ionisation parameter and Fe ion average charge comparisons for tpho and pion for X-ray WA component 0 of NGC 3783 for three different densities (10¹⁰, 10¹¹ and 10¹² m⁻³ from top to bottom). In the left panels, the black dots represent the ξ values of pion that are needed to obtain the same Fe average charge as for the tpho model. ξ_TPHO is a luminosity-dependent quantity in tpho calculations (See Eq. (16)). The red line represents the condition where the log ξ from pion is equal to tpho. The right panels show log ξ versus C_Fe, where the blue dots represent the pion log ξ and red dots represent the tpho log ξ, respectively.