Total fraction of obscured AGN with log N_H > 22 (left panel) and log N_H > 23 (right panel) vs. redshift for different combinations of large-scale (ISM) and small-scale (torus) obscuration. All curves are for δ = 3.3 and ϵ = 0.25. The characteristic surface density Σ_c, * of ISM clouds is assumed to evolve as ∝(1 + z)^γ, with γ = 2 (blue curves) or γ = 3 (red curves). Short dashed lines refer to ISM-only obscuration (i.e., no torus considered, as in Fig. 11). Long dashed and solid lines show the total obscured AGN fraction when adding a torus with half-opening angle θ_torus = 45° and 60°, respectively. The horizontal dotted lines show the obscured AGN fraction expected by torus-only obscuration.