Frequency dependence of absorption cross-sections for an electric field parallel to each axis of an ellipsoid normalized by |$8 \pi ^2 \mathcal {V}$| (top panel), of relative absorption cross-sections for an electric field parallel to the semi-middle and semi-minor axis to that of the semi-major axis (middle panel), and of the real and imaginary parts of the electric susceptibility for spherical dust (bottom panel). A ratio of geometric factors is fixed to |$L_x : L_y : L_z = 1 : 2 : 3$|⁠. Other parameters are set to the best-fitting values for W 43 listed in table 2.