PDR model results of the non-clumpy globule tail model. Left panel: ¹²CO (blue points and line) and ¹³CO (red points and line) model SLED (spectral line energy distribution). This is the best-fitting non-clumpy model. The colour-shaded areas give the range of models by varying all parameters by ± 20%. Right panel: observed (blue) and modelled (red) fine-structure line fluxes for this model, with the model variations indicated by the vertical red bands. Data points without error bars, namely, the two highest-J ¹²CO lines J = 10→9 and 9→8), are excluded from the fit, but shown to provide further information.