M_HI/M_∗ (upper panel) and M_H2/M_∗ (middle and lower panels) ratios versus stellar mass. CLUES simulated galaxies are shown as red squares, while the various observational samples take the symbols shown in the legend. HI and H₂ masses are calculated by GRASIL-3D based on a log-normal PDF for gas densities. The middle and lower panels differ in the assumption for the observed galaxies of a metallicity-dependent or constant CO-to-H₂ conversion factor, respectively, which in GRASIL-3D means the use of different density threshold values ρ_mc,thres in order to match observational data.