Behavior of ionization parameter, electron temperature, C IVλ1549 luminosity, and ionic fraction as a function of radius for density value log n_H = 9.5 [cm⁻³], and for the two adopted SEDs for the low (top panels) and high-z (bottom panels) samples. Top, upper panel: behavior of the ionization parameter (left axis scale, blue dots) and electron temperature (right axis scale, green dots) as a function of radius for a M_BH = 10⁹ M_⊙ radiating at Eddington limit and illuminating a slab of gas. We assume column density N_c = 10²² cm⁻², Mathews & Ferland (1987) SED, and the metallicity five times solar in all cases. Top, lower panel: logarithm of C IVλ1549 luminosity (black dots) and ionic fraction as a function of radius. The blue and red line represent the ionic stages higher and lower than 3, respectively, and the black circles ionic stage 3. Bottom, upper and lower panels: same as top panels, for log M_BH= 9.5 [M_⊙], and SED from Krawczyk et al. (2013). In both the top and bottom panels, the horizontal gray bands indicate the range of ionization parameters consistent with the observed C IV equivalent width and the C IV/Hβ ratio. The vertical bands represent the corresponding range of permitted radii.