Locus (see Eq. (8)) for the formation of a GW source through stable MT with a 30 M_⊙ donor as a function of the CO accretor mass, m_a, i, and orbital period, P_i. The solid curves represent the upper bounds on initial periods log P_i, to achieve a delay time of t_merge = t_H; different stripping factors, α_core, are labeled along the corresponding curves. Colored diamonds correspond to the point, along their respective curves, at which the MT episode is expected to invert the mass ratio.