Predictions of N_H variability assuming a clumpy wind model with the total number of clumps per flow time N and varying terminal porosity length h_∞. Shown are 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. For the case of N = 1000 see Figs. 9 and A.1.