Wavelength-dependent emission ratio between the source function of indirectly-heated clouds S_ν;IH and the hot face of directly-heated clouds S_ν;DH(φ = 0°). The various lines represent different distances r from the AGN with r = 1, 1.5, 2.5, 4, 7, 10, 15, 25, 40, 70, 100 and 150 r_sub from top-red to bottom-blue. The left panel shows simulation results for “ISM standard” dust with Ossenkopf et al. silicates, the middle panel presents “ISM large grains”, and the right panels shows “Gr-dominated” dust.