Contour plots of the JED temperature (solid lines) and optical depth (dashed lines) in the ξ − b plane at a distance of 10 R_G from a 10 M_⊙ black hole. The ratio of the outer to inner JED radii is taken equal to 100, and the total accretion rate for the computation of the disc thermal balance is fixed to 1% of L_Edd, i.e., the typical luminosity of Cyg X-1. The grey and dark grey areas correspond to the regions that agree with the observational constraints reported in Fig. 3.