Evolution of the mass ratio, semi-major axis, and ζ_L computed using an analytical orbital-evolution prescription (Eqs. (1) and (2)), for an initial mass ratio M_a/M_a = 0.275. The colours and styles of the curves correspond to different mass-transfer efficiencies, as indicated in the legend. Vertical lines indicate when the quasi-adiabatic instability criterion (see Temmink et al. 2023) is reached in our MESA simulations of a binary with the same values of β and initial mass ratio, an initial donor mass of 5 M_⊙, and an initial period of about 7 days (see Appendix B). Mass transfer is stable in the fully conservative case.