Ratios F_a,c/F_a,cs as a function of optical depth τ and the effective radius a_eff of the gamma size distribution for three different effective temperatures of the central star: 7300 K (upper diagrams), 5800 K (middle diagrams), and 3000 K (lower diagrams). Results are shown for calculations using DISORT (left column) and two-stream methods (right column). The same colour scheme is used in each diagram. (This figure is available in colour in the electronic form.)