Dependence of BH accretion on the energy efficiency of specific feedback mechanisms for the 10⁶ M_⊙ (top panel) and 10⁸ M_⊙ (bottom panel) GMCs. We summarize experiments with fixed-value energy efficiencies (solid) and show the scaling relation (dashed) based on Eq. (4). Several more sophisticated subgrid models are also displayed for reference, and for each of them the energy efficiency is calculated at the hyper-Eddington regime of f_Edd = 1000.