Left panel: mean density vs core conditions indicator (t_u) plot. The inversion results are plotted in orange with their respective error bars. The × are values for the reference models computed with the Levenberg-Marquardt algorithm without extra mixing. The □ are related to models with a decaying exponential turbulent diffusion coefficient starting at the bottom of the convective enveloppe. The + show models with a decaying exponential diffusion coefficient starting from the surface and the ◇ use a constant turbulent diffusion coefficient. The ∗ depict models using the new OPAS opacities and the decaying exponential coefficient starting from the surface. Right panel: surface chemical composition box for 16CygB. The colour code allows direct trend comparisons between the surface chemical composition and the t_u and values as in Fig. 3.