Scaling of the photon index Γ versus the normalization N_BMC for M101 ULX-1 (with red points – target source) and 4U 1630-472, XTE J1550-564, and H1743-322 (with pink, blue, and green indicating the reference sources), respectively. The bright blue vertical arrow schematically shows that the parameter A is the value of the index saturation level. The horizontal black arrow stresses the fact that the correlations of the target and reference sources are similar. The only difference is in terms of the BMC normalization because of the different values of the M_BH/D² ratio.