Corrected dielectron yields as a function of $S/B$ in two different mass intervals, i.e. 0.18-0.5\,\GeVmass (left panel) and 0.5-0.7\,\GeVmass (right panel), for $0.2 p_{\rm T,e} 10$\,\GeVc and $|\eta_{\rm e}| 0.8$ in the 10\% most central Pb--Pb collisions at \fivenn. The red curves show the expected dependence assuming a bias of the estimated background of the order of $\pm 10^{-4}$ ($b = -10^{-4}$ in Eq.~\ref{sysb}).