Impact of structure on the radial intensity profiles. Shown are azimuthally averaged radial intensity profiles for C¹⁸O J = 2−1 for models with an inclination of 45° at different times in the post-burst phase. Density structures from left to right: rotating envelope with a disk component, rotating envelope without a disk, a spherical symmetric envelope (all models include an outflow cavity). The large dot in each profile indicates the R_50% radius corresponding to the value given in the legend.