Exploration of the parameter space of the hot dust structure model. The colour maps show the derived R_OI/R_RM ratio based on different α and β in grids. The four columns present the model with different inclination angles (i from 0° to 40°). The geometric covering factor of the model is labelled on the left. A fiducial model, which can qualitatively explain our observed R_OI/R_RM ≈ 2, is indicated by the cyan star.