Predictions of the AGN NLR models described in Sect. 4.1 in the C IV/He II vs. C IV/C III] (top left), C III]/He II (top right), N V/C IV (bottom left) and N V/He II (bottom right) diagrams. Each panel shows data measurements with error bars and upper limits (black symbols) of the C IV-selected type 2 AGN, described in Sect. 3, and AGN models (shaded areas) encompassing wide ranges in power-law index, α, ionization parameter, ⟨U⟩, gas metallicity, Z, gas density, n_H, and dust-to-metal mass ratio, ξ_d. The purple and orange shaded areas indicate AGN models with no microturbulence velocity and an inner radius of 300 pc and models with microturbulence velocity v_micr = 100 km s⁻¹ and an inner radius of 90 pc, respectively. Cyan stars show the predictions from photoionization models of star-forming galaxies of Gutkin et al. (2016). In each panel, the gray arrows indicate the effect of correcting the AGN data by dust attenuation for a galactic attenuation curve (Cardelli et al. 1989) and A_V = 1 mag.