Our parameterisation of the hydrogen abundance profile and the three global stellar parameters that we also consider. The parameters in the figure are the mass (M_total), the metallicity (Z), the rotation Ω/Ω_crit, the central and surface hydrogen abundances (X_c and X_s), the normalised mass coordinates at the outer boundary of the composition gradient and the convective core (M_μ and M_c), and the curvature parameters α, f_a, and f_b.