Variation of non-LTE effects on the N(CH₃OH)/N(c-C₃H₂) abundance ratio at different volume densities. The intensities of the 2_1,2–1_1,1 (E₂) methanol line and the 2_0,2−1_0,1 cyclopropenylidene line were calculated using RADEX at different volume densities, and assuming different ratios (shown as a horizontal dashed line in each panel). The parameters used for the RADEX calculations are shown at the top of each panel. The red crosses show the abundance ratios resulting from the column densities that have been calculated to reproduce the intensities derived with RADEX, assuming LTE and T_ex = 10 K.