Left: best-fitting model SED (purple solid line) consisting of the stellar and present-day wind contribution (grey dotted line), a detached-shell contribution of 0.1 μm grains (purple dashed line), and an additional shell contribution of 0.25 μm grains (magenta dot-dashed line). The wind parameters are 2 × 10⁻¹⁰ M_⊙ yr⁻¹ in 0.1 μm sized grains for the present-day wind, 3.00 × 10⁻⁵ M_⊙ in the 0.1 μm grain shell, and 1.05 × 10⁻⁶ M_⊙ in the 0.25 μm grain shell, derived for solid sphere amC grains. Right: χ-square map for the grid of different shell masses for small (0.1 μm) and large (0.25 μm) sized grains. The grey contour shows the 1σ level on the best-fitting χ-square value.