Contour representation of the log λ_Edd − log R_Fe plane, showing the density distribution of sources for each of the three samples. Black, blue, and red dashed lines are our best-fit linear regressions to datasets from Hu et al. (2008), Wu & Shen (2022), and N+25, respectively. Slopes and intercepts are shown with their 95% confidence intervals (∼2σ); numbers in brackets are the RMS scatters of each sample about the respective best-fit lines. We note that λ_Edd and ṁ are used interchangeably (see Appendix B).