Summary of the minimum distance, the UV-reprocessed luminosity, and the intensities predicted with a sole distribution of PDR models for the PDR-only scenario. Panel (a): Minimum distance as a function of the gas density. The dashed line represents a 0.5 dex limit (i.e., a factor of three difference between observed and modeled line intensities) to guide the eye. Panel (b): UV-reprocessed luminosity as a function of the gas density. The orange shaded area represents the SED estimation of the reprocessed UV-luminosity (see Appendix C). Panel (c): Comparison between the observed line intensities and those obtained for the model at n_H = 10³ cm⁻³, b = 0.1, G₀ = 10. The observations are presented as blue stars (see Table B.2) and the modeled intensities are shown as open black circles. In the lower panel, the residuals are shown as orange squares. The dashed and solid lines give the ± 0.5, 1 dex limits, respectively.