Ratio of the dust A^BB and A^EE angular power spectra amplitudes computed on the 352 patches at high Galactic latitudes (described in Sect. 5, circles), as a function of the mean dust intensity ⟨I₃₅₃⟩ of the patch. The mean value, ⟨A^BB/A^EE⟩ = 0.51 ± 0.18 here, is represented as a dashed-blue line and the associated ± 1σ dispersion as a light blue shaded area. The A^BB/A^EE ratio for the M_B2 spectra presented in Sect. 6.3 is shown as an orange diamond.