Stacked radial profiles of the neutral atomic hydrogen density column (N_HI, single lines) compared with ISM proxies of the total hydrogen density column (N_H, lines with errors) for three intervals of increasing N_HI values. N_HI profiles radially average patches of the all-sky HI4PI survey. N_H proxies, N_H ≡ ϕ(I_⟨s(857)⟩), are inferred from HFI measurements of the dust emission at 857 GHz, which we corrected for local variations in the dust SED (see also Eqs. (3) and (6)). The shaded areas depict the dispersions of differences between N_H and N_HI values. The error bars depict the uncertainties on the average values of these differences.