Top left panel: Column density of the total covering cold absorption vs power-law photon index, fitted only in the 4-5 keV and 7-10 keV energy bands. The correlation among the values is assessed at ≫5σ for both the unobscured and obscured epoch. Top right panel: Column density of the partial covering cold absorption vs power-law photon index, fitted in the 4-10 keV energy range. The degeneracy between the two parameters is not present in this case, with a correlation probability ≲20%. Bottom left panel: Covering fraction of the partial covering absorber vs power-law photon index. Bottom right panel: Covering fraction vs column density of the absorber. Data relative to unobscured and obscured epoch are reported in yellow and green respectively.