Attenuation curves of the best-fit radiative transfer models for a dust ring geometry. The THEMIS MW dust mix produces a steeper curve (blue line) than a dust mix with only bare silicate grains (orange line). The dashed lines correspond to the corresponding intrinsic extinction curves of the dust mixes, normalised to the model attenuation at 5509 Å. The observed attenuation curve of FCC 167 (from Sect. 3) is shown in black.