(a) Near-IR size–luminosity diagram of our observed sample of MYSOs. The measured inner ring size R_in of the observed MYSOs (GRAVITY, AMBER; based on Table 3) is plotted with respect to the stellar luminosity. The shaded area represents the dust sublimation radius R_s as predicted by the presence of a disc with an optically thin cavity for a range of temperatures. The adopted dust sublimation temperatures are 1000 K (solid line) and 1500 K (dotted line). (b) Same as before but overplotted with two MYSOs with K-band measurements from the literature (filled black stars; IRAS 13481-6124, NGC 2024 IRS2, Kraus et al. 2010; GRAVITY Collaboration 2020a) and with indirect measurements (star symbols; modelled sizes presented in Frost et al. 2021). The open and filled stars represent the sources for which the modelled inner radius was found to be larger than or equal to R_s respectively. The dust sublimation radius as predicted by models of different dust temperatures with (blue area) and without (yellow area) backwarming effects is also overplotted. (c) Same as before but including the available measurements of Herbig AeBes and T Tauris from the literature. The dust sublimation radius as predicted by the classical scenario of a flat optically thick disc is also overplotted.