Size-luminosity relations and spectral indices dependent on disk sizes. In (a) and (b), the fluxes are divided by the cosine of the inclination (i = 20 Å). The plotted 68% emission disk radii are found to decrease from low (0.30″) to high (0.04″) resolution for all models irrespective of wavelength which is highlighted by lines connecting both radii. The grey dashed lines show the relations for Lupus at λ = 1.3 mm and λ = 3.0 mm found by Tazzari et al. (2021a), where the grey area represents the 68% confidence interval around the median. (c) Spectral index (α_1.3–3.0mm) over disk effective size (R_d,68%) at λ = 1.3mm with 0.30″ resolution, black dots show Lupus data also from Tazzari et al. (2021a).