Fraction of [C II]158 μm in the ionized phase vs. metallicity. The single-sector, density-bounded models represented by orange stars pointing down are PDR-deprived; all their [C II] emission arises from the ionized gas (log f[C II]_H+ ∼ 0). The underlying KDE represents the distribution of all the MCMC draws for galaxies with N_sectors ≥ 2 only and ρ the associated Spearman correlation coefficient. The dashed line represents the relation derived by Cormier et al. (2019) for the DGS, assuming a fixed electron density n_e = 30 cm⁻³.