Statistics of the effective disk radius R68 from the model grid. Upper panel: ranges of R68 for each of the sampled R_c. The blue lines refer to the result when porous dust grains are considered, whereas the grey lines represent the case by using compact dust opacities. The thickness of lines is only for a better illustration. Bottom panel: relation between R68 and F_0.88mm. The blue curve and grey curves enclose the regions occupied by the 9360 models with porous grains and compact grains, respectively. The dashed line shows the relation log R68 = 2.16 + 0.53 log F_0.88mm (Hendler et al. 2020). The red dot indicates the expected position of IRAS 04370+2559 in the diagram; for details, see Sect. 4.2.