Expected line ratios as computed by RADEX for H₂CO (top) and CH₃OH (bottom) for a column density of 10¹⁴ cm⁻². The white contours indicate the observed values and the dashed lines the uncertainty. The coloured lines indicate the ratios as computed for our DALI models of the settled model for fixed abundances of 10⁻⁷ and 10⁻⁹ in specific emitting layers, as described in the text.