Radiative efficiencies of the BH populations at redshift z = 0, as a function of mass, for the Box4 run. The triangles show the collection of empirical estimates of the radiative efficiency by Daly (2021). The dotted, dashed and dash-dotted lines mark the values of the efficiency corresponding to a = −1,0,0.998, respectively, for reference. The population in the bottom part of the figure represents the BH that are accreting in counter-rotating conditions.