Panels showing the evolution of the exemplary ‘System 2’ binary model from Paper I, with initial parameters: M_T, i = 26 M_⊙, P_i = 1.0 d, and q_i = 0.8. The parameters from top to bottom panels are: the fill-out factor (R/R_RL), the temperature and mass ratio (T₂/T₁; q), orbital period (P), mass of both components and the mass-transfer rate. Also shown are the contact (light-green region) phase and near-contact (pink region) phase, which is further divided into the detached phase (crosshatching) and semi-detached phase (striped hatching). The open circles are the instances at which synthetic PHOEBE light curves are computed (Fig. 5).