Internal profiles of Star 2 in the example system (M₁ = 100 M_⊙, q_i = 0.7, P_i = 1.5 days) showing the total diffusion coefficient, D_tot (left panels), and helium mass fraction, Y (right panels), as a function of Lagrangian-mass-coordinate. The star in the Standard Grid is marked in green and that in the Enhanced Grid in black. Top panels: profiles at an age of 0.27 Myr, as marked by a cross in Fig. 4, bottom panels: age of 0.80 Myr, as marked by a diamond in Fig. 4. The grey dashed line in the right panels represents the initial helium mass fraction, Y₀.