Variation in e-folding radius of the CS abundance profiles with circumstellar gas density. The dashed cyan line (Maes et al. 2023) is from chemical modelling results, while the other trends plotted are calculated from RT models. The magenta point is obtained from chemical modelling results (Van de Sande et al., in prep.), for a star of MLR 1.0×10-5 M_ʘ yr⁻¹ and a ν_∞ of 15 km s⁻¹, and the corresponding uncertainty range is estimated from sensitivity calculations on chemical models (see text). The rightmost blue circle is for AFGL 3068, and is likely underestimated (see text).