Top: semi-empirical values Q_c of the convective core mass at the ZAMS (normalized to the total mass) for each of the stars in our sample. Triangles represent components of systems with age differences exceeding 5%. The dashed line is a third-order polynomial fit drawn to guide the eye. The solid line shows the trend of Q_c with mass for solar-metallicity ZAMS models having α_ov = 0, for reference. Bottom: fractional increase in Q_c over that indicated by the solid line in the top panel, expressed as a percentage.