Mass-ratio (q) distributions of BBHs formed through the MRR channel for different binary-evolution models. Left: models adopt the fiducial mass-transfer prescription, lognormally distributed natal kicks with (μ = 5.6) and (σ = 0.68), with different common-envelope efficiencies, α_CE. Middle: models with the same natal-kick prescription, different mass-transfer prescriptions, and assuming α_CE = 1.0. Right: the same mass-transfer and natal-kick models as in the middle panel, but for α_CE = 5.0.