Sketch of the hot dust structure model. The hot dust emission is in yellow. The cloud radial distribution follows a power law with the index α, and the cloud height above the midplane is close to a power-law function controlled by β. Panel a shows the model with β ≈ 0, while panel b shows a model with β > 0. We show the models in an edge-on view with the observer to the positive direction of h to illustrate the ‘foreshortening effect’. In this way model (a) has R_RM ≈ R_OI, while model (b) has R_RM < R_OI.