Orbital separation of BH–He-star binaries post SMT for accretion efficiency limit η_acc ∈ [1, 10⁵, 10⁹] (in units of Eddington-limit) represented with solid lines according to the legend. The histogram has units of M_⊙ Gpc⁻³ and accounts for the total stellar mass formed per comoving volume integrated over the Universe cosmic history per log-orbital period bin. The grey shaded area represent the 90% CI of the systems forming merging BBHs with T_merger < 14 Gyr for the model with η_acc = 1 (the other models have similar CIs). As the accretion efficiency is increased, the orbital separations become larger and the distributions move to the right: for highly super-Eddington accretion efficiency η_acc = 10⁹ the tail almost exits the grey area, hence, decreasing the merger rate.