Contours of the warm corona temperature (blue lines) and the warm corona spectral photon index (black dashed lines) in the planes from left to right: χ–T_bb, χ–n_H, and χ–ξ₀. When T_bb, n_H, or ξ₀ are not variable they are fixed to T_bb = 10⁵ K, n_H = 10¹² cm⁻³, and ξ₀ = 10³ erg s⁻¹ cm. The corona optical depth τ_cor is fixed to 20. The background colors correspond to the Compton cooling to corona heating fraction whose color scale is reported on the right. Similarly to Fig. 2 the green line corresponds to the condition χ = 1.