Effect of different parameters on the spectral hardness of equilibrium solutions at an inclination of 60°. In each panel, a single parameter is varied while keeping all others fixed at their reference values, as described in Section 3.1. The reference parameter set (black hole spin a = 0, coronal electron temperature T_e = 120 keV, and disk albedo = 0.5) is shown by black circles in all panels. Panel (a), (b), and (c) shows the effect of black hole spin, coronal electron temperature, and disk albedo respectively. In general, higher spin, higher electron temperature, and higher albedo lead to harder spectra at a given optical depth. However, among these, only increasing the albedo results in a significant reduction of the minimum photon index Γ_min.