Comparison of observations with the prediction of line intensities as a function of n_H and G₀ from an updated version of the Kaufman et al. (2006) PDR models (Wolfire, priv. comm.). For all positions except for (32,−23) and (60,−45), the [¹³ C II] intensities are beyond the values predicted by the models. The horizontal dashed lines correspond to the values of G₀ estimated from the FIR intensities (lower) and from the stellar FUV radiation scaled only by geometrical dilution due to the increase in distance from S 1.