Ring half-flux radius vs. luminosity for group I (blue), group II (red) and unclassified (black) targets. The dashed and dotted lines show the relationship for the labeled temperature and cooling efficiency of the dust ϵ_g of an optically thin inner cavity model. The inset shows the distribution of values of the dust cooling efficiency ϵ derived from our ring half-flux radii and dust temperatures. The empty symbol (source #26) corresponds to R CrA, a low-quality source in Vioque et al. (2018). The numbering refers to Table 1.