Size-luminosity diagram of all Class II disks in Lupus, based on data from Ansdell et al. (2018), Tazzari et al. (2021), and van der Marel et al. (2022) (disks around M dwarfs, present fluxes less than ~90 mJy). The R₆₈ parameter refers to the size of the dust disk, which is typically measured with a curve-of-growth method, encircling 68% of the total flux (Hendler et al. 2020). F_1,3mm is the observed flux and i represent the inclination of the disks with respect to the observer. The expected trend for drift-dominated disk models from Rosotti et al. (2019) is shown with a dashed line. Other than two resolved compact disks of 3-5 au radius from high-resolution observations in van der Marel et al. (2022) (purple dots), the majority of compact disks are unresolved with an upper limit of <20 au on their radius (red triangles). Considering the trend in the plot as well as the predictions from drift models, in reality most of these disks are expected to be 2-10 au in radius.