RADEX fit χ² surface (for the “Set 1” line ratios, assuming the Gaussian-derived beam correction factors) as a function of N_12CO and Gaussian FWHM θ_s in the left panel, The RADEX models shown here have ΔV = 20 km s^-1; the associated χ² values are shown as a side-bar color table. The best-fit values are shown as an open (white) circle; the error bars shown consider a slightly more limited range in χ² respect to Table 6.