Correlation between the CO gas radii and the integrated (left) and peak (right) fluxes. The ¹²CO-, ¹³CO-, and C¹⁸O-based data are shown from bottom to top. The size of the disk symbol reflects the disk emission size for the given CO isotopologue, and the color of the symbol designates the luminosity of the central star (darker colors correspond to lower luminosities). The coefficients of determination (corresponding to the Pearson coefficients r to the power of two) were calculated by taking the data uncertainties into account and are shown in the top right corner of each subplot.