Same as right panels of Fig. 11, but only for relations with Σ_mol and separated into the different environments. We note that fitting the binned averages as function of Σ_mol results in slopes that are within 5σ to a slope of zero for all line ratios as function of Σ_mol, except for the ring environment, where the slopes are significantly negative. The slopes for the HCN-, HNC- and HCO⁺-to-N₂H⁺ line ratio as function of Σ_mol in the ring environment are −0.63 ± 0.04, −0.48 ± 0.04 and −0.46 ± 0.04, respectively.