Cumulative distribution functions of the RV separation (ΔV_r) between the two stars in a binary system, ratio of temperatures (T₁∕T₂), ratio of radii (R₁∕R₂), and the relation between T₁∕T₂ and R₁ ∕R₂ in the fourth panel. The distribution of ΔV_r is cut at the lower level of 15 km s⁻¹ as explained in Sect. 6, while R₁∕R₂ starts at unity by construction because we define the primary as the star with a larger radius.