Dereddened NLR ratios of [O III]/Hβ versus R_OIII for the same observational dataset as in Fig. 4. The gray dotted line consists of radiation pressure stratified ionization-bounded models with U_o = 0.1 assuming the Fg97 SED with T_cut = 10⁶ K. The frontal density along the sequence varies from up to 10⁷ cm⁻³, in steps of 0.5 dex, as in Fig. 7. The blue continuous line corresponds to a similar density sequence but assuming the presence of temperature fluctuations at the level of t² = 0.15. The light-green arrows describe the change in R_OIII ratios for the models with frontal densities of and 10^3.0 cm⁻³, respectively.