Predictions of N_H variability assuming a clumpy wind model with the total number of clumps per flow time N = 1000 and the terminal porosity length h_∞ = R_∗ (see Sect. 4.1.3 for explanation of parameters). Left: model histograms for the distribution of equivalent absorption column density N_H. Right: average values (circles) and standard deviations (error bars on the average values) in a given orbital phase for the theoretical model (red) and values measured in the hard state of MJD 53 900−55 375 (black). Average measured values are shown as “average − N_H,ISM” to account for the ISM absorption.