2D cutoff of the likelihood distributions of the parameters describing the shock and the PDR distributions obtained for a Gaussian distribution of shock velocities. The parameters are the total shock solid angle Ω_S, the central shock velocity μ_vs and the dispersion of the shock velocities σ_vs, and the PDR total solid angle Ω_P. The color code represents the distance in dex units. The 0.5, 0.7, and 1.0 dex limits are highlighted with dashed black lines. The straight black dashed lines and the black points indicate the position of the global minimum. The gray areas represent the regions where the assumption on the radiative transfer regarding cross-absorption between surfaces breaks down. The criterion is more stringent for the [OI] 63 μm line (gray area above the white solid line) than for the [CII] 158 μm line (gray area above the white dashed line), and is always fulfilled for the H₂ lines (see Appendix A).