Origin of partial envelope stripping of the LMC and SMC models explained based on the response of donor stars to mass loss, using the 20 M_⊙ donor case as an example. Quantities are plotted as a function of the remaining donor mass M_don, meaning the time direction in the top two panels is to the left. Top panel: mass transfer rate from binary models (P_ini ≈ 32 days). Middle panel: equilibrium radius R_th; eq that the donor star would need to have in order to be in thermal equilibrium, compared with its Roche lobe size R_RL. For as long as R_th; eq > R_RL, the thermal-timescale mass transfer continues to strip the envelope of the donor. Vertical dotted lines mark the points when R_th; eq = R_RL, the donor can regain equilibrium, and the mass transfer may stop or slow down to the nuclear timescale. Bottom panel: internal He abundance profile of the donor at the onset of RLOF.