As in Fig. 4, but for a fixed spectral image value of Γ = 1.85. The trend is similar to that found previously, although the differences are now dampened. The light green area represents the constraint from IXPE observations of NGC 4151, while the dark green area indicates the constraint resulting from the combination of IXPE observations and BLR reverberation. Both the constraints are given at the 68% confidence level.