Comparison between the distributions of the polarization fractions p and logarithmic column densities in the simulations (colour scale, all viewing angles combined, with upper and lower envelopes in solid red lines) and those of the observations in the selected fields (solid black lines). Note that the latter are restricted to N_H> 10²¹ cm^-2. Dashed lines are linear fits of the form on the distributions’ upper envelopes, restricted to a common range of column densities 2 × 10²¹ cm^-2<N_H < 2 × 10²² cm^-2.