Possible scattering mechanisms producing the polarisation in the continuum that we observe. We only display one cone (the lower cone but mirrored with respect to the orbital plane) since the scattered light is mostly generated there (i.e., the larger the distance from the central object, the lower the density and the intensity of the radiation field). Grey dots represent the scatterers. The spikes of the nebula are traced in black dashed lines, the central system is represented in orange, the horizontal line representing the accretion disc. The observed linear polarisation is displayed in red. Case a) depicts the scattering produced at all points of the cone (i.e., the wide jet mechanism). The expected theoretical polarisation in this case is represented as a short-dashed orange line. Case b) displays the case where the scattering occurs at the aperture θ that gives a polarisation that is compatible with the observed one.