RADEX fit of the χ² (logarithmic) surface of the [Ci]/¹²CO fits as a function of n_H2 and N_CI(1−0); the left panel shows the intensity fits (Eq. (4)) and the right the ratio ones (Eq. (5)). The RADEX models shown here have ΔV = 20 km s^-1. The associated Log(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.