$R_{\rm {PbPb}}$ of electrons from heavy-flavour hadron decays in centrality bins of Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. The solid band at $R_{\rm {PbPb}}=1$ brackets the uncertainty on the average nuclear overlap function ($\langle T_{\rm{AA}} \rangle$)