Same as Fig. 1 but over-plotted with isochrones with an age of 4.5 Gyr and metallicity [Fe/H] = 0. Four primary masses (0.7, 0.75, 0.8, 0.85 solar mass) are positioned on the isochrone. For each isochrone, binaries of different mass ratios are simulated and colour-coded by their mass ratio, q. The binaries with q = 1 appear on the upper strip, positioned 0. 752 magnitudes above their lower-strip single primaries. Isochrones are derived from the PARSEC models (see the main text). The red line separates the two strips; the line equation is −0.44 × x² + 4.3 × x + 1.37. It is generated based purely on the M_G,0 histograms, as explained in Section 2.1. For a similar simulation, see Fig. 1 in Wallace (2024).