Percentage of initial captures as a function of different parameter pairs, marginalising each time over the three others. Top-left panel: as a function of the mass of the inner BH (M₁) and its initial radius (r_i); bottom-left panel: as a function of the mass of the outer BH (M₂) and r_i; top-right panel: as a function of M₁ and the initial radial separation between the BHs (Δr_i); bottom-right panel: as a function of M₂ and Δr_i.