Both panels: Marchant et al. (2021)M_donor = 30 M_⊙ grid with the POSYDON grid at M_donor ≈ 33 M_⊙ at 0.1 Z_⊙ overlaid. Generally, the grids overlap well, although POSYDON marks L₂ overflow as unstable. Top panel: POSYDON STAR+BH population with M_donor = 33 M_⊙ ± 2 M_⊙ that has undergone Case B mass transfer in the STAR+STAR phase is overlaid. There are no systems in the SMT merger region from Marchant et al. (2021) that do not fall within the SMT region of POSYDON. Bottom panel: Artificial STAR+BH population where all the mass lost by the primary during the STAR+STAR phase is added to the ZAMS mass of the secondary and the orbit is adjusted analytically assuming fully conservative mass transfer and no wind loss. This approximate approach shifts lower-mass companions into the 30 M_⊙ ± 2 M_⊙ regime with wider initial orbits.