Black hole mass evolution of a black hole with M = 10¹⁰ M_⊙ at z = 6.3, assuming a continuous accretion on a Salpeter timescale at the Eddington limit (solid lines) and at f_E = L_d/L_Edd = 0.4, i.e. close to the Eddington ratios derived for the two sources following the KERRBB approximation for a maximally spinning black hole (dotted, dashed, and dot-dashed lines). The colours refer to different accretion efficiencies and combinations, as indicated in the legend. Next to each line, the labels show the mass values of the hypothetical seeds located at z = 20 for each accretion setup.