Details are the same as in Fig. 9, but displaying the relative fit residuals (250 µm residual minus 500 µm residual) in region C. Red symbols correspond to cases where the 250 µm emission is underestimated and 500 µm emission is underestimated towards the main core. In the case of the blue symbols the situation is reversed: with larger LOS extent and large external extinction, the models overestimate rather than underestimate the dust temperature in the core.