Profile of the hydrogen abundance, X, as a function of the normalised mass, for the target t1 model in blue and the best-fit model of the t1-asp-5freq (and t1-asp-4freq) exercise in orange. The vertical dashed lines indicate the limits of the fully mixed central region (i.e. including the overshoot region) of the two models, with the same colour association than the X profile. The vertical dotted lines are similarly colour-coded and indicate the limits of the gradient of chemical composition.