Distributions of the normalized absorption column density as a function of the normalized flux (1–10 keV) measured from the HR-resolved spectral analysis for the five sources in Sect. 2 (see text for further details). The previously published XMM-Newton data on the outburst of IGR J17544-2619 (Bozzo et al. 2016b) and the bright flare from IGR J18410-0535 (Bozzo et al. 2011) are also included. All uncertainties are at 1σ confidence level.