Parameter window for BBH mergers from SMT evolution across different BH masses. Here, we plot the outcome of binary MESA models marking BBH mergers with star symbols, assuming fiducial AM loss (γ = γ_BH) and different primary BH masses M_BH; 1. Color indicates the final fate: wide BBH system (light yellow), merging BBH system (colorscale indicating the delay time), unstable MT with a convective donor (red), unstable MT with a radiative donor, likely leading to a BH + star merger (grey), close non-interacting systems due to chemically homogeneous mixing or very strong winds (white dotted). In the top two rows, the blue line marks the boundary between MS and post-MS donors. In the bottom two rows, only a limited range of periods is computed and all the donors are on the MS. The grid is constructed based on the initial mass ratio M_BH; 1/M_star in steps of 0.02.