Top panels: 3.3 μm band centre as a function of the distance from the star. Middle panels: 3.3 μm FWHM as a function of the distance from the star. Bottom panels: 3.3 μm FWHM over the band centre. For HD 100546, which is shown in the left panels, values are reported from THEMIS varying band gap from 0.1 eV (magenta) to 0.6 eV (red, as rainbow colours). Top two panels: size increases from bottom to top (for the same colour). Bottom panels: size increases from right to left.