Density plot of BH binaries with noncompact companion together with BH-BH progenitors (black points) in a grid of the system mass ratio and orbital period. Results only for the SMT subchannel. Left panels systems with Z = 1% Z_⊙, right panels with Z = 10% Z_⊙. The top two panels are with BH-star predicted for our default model, which includes the extra instability for tight BH-star binaries. The bottom panels are BH-star binaries formed in the model without the extra instability, which allows tight systems to proceed with SMT instead. This model, in contrast to our default one, produces a fraction of tight BH-star binaries (P < 5days) and equal mass ratios. It also allows some of those close BH-star systems to later evolve into BH–BH mergers. Results only for SMT channels, without systems that evolved (or would evolve) through a CE.