The dependence of $\Delta \gamma_{1,1}$, $\Delta \gamma_{1,2}$ and $\Delta \gamma_{2,2}$ on centrality, measured in Pb--Pb collisions at $\sqrt{s_\mathrm{{\rm NN}}} = 2.76$ and 5.02 TeV. The data points for $\sqrt{s_\mathrm{{\rm NN}}} = 5.02$ TeV are shifted along the horizontal axis for better visibility.