Equivalent width of the iron Kα line versus the X-ray luminosity obtained simulating a torus with an equatorial column density of and a covering factor decreasing with the luminosity. The θ_OA − L_X relationship used here is that of Hasinger (2008; see Fig. 2). The relations of Bianchi et al. (2007, black dashed line) and Shu et al. (2012, blue line, obtained averaging different observations of the same source) are also shown for comparison (see also Table 1). The normalization of the relation of Bianchi et al. (2007) has been fixed to an arbitrary value for comparison.