Time delay (t_del [Myr]) versus mass ratio distribution of BH-BH systems in four tested models. The red dashed line corresponds to 14 Gyr. Top-left panel: BH–BH mergers formed via an SMT subchannel in our default model with revised mass transfer stability criteria. This model includes fallback, decreased natal kicks, and low angular momentum loss during nonconservative mass transfer. Top-right panel: BH-BH binaries formed via the SMT subchannel in the model with revised mass transfer stability criteria and low angular momentum loss but non-fallback decreased natal kicks. Bottom-left panel: BH-BH systems formed via the SMT subchannel in the model with revised mass transfer stability criteria and fallback-decreased natal kicks (as in our default model) but high angular momentum loss during nonconservative mass transfer (γ = γ_L2). Bottom-right panel: BH–BH mergers formed by both the CE with α = 1.0 (dominant) and the SMT (subdominant) subchannels in the model with old criteria for mass transfer stability.