Comparison of hydrogen column densities of this paper with those calculated according to the WCZ models of Paper I. Top panels show examples of models J and M (Eq. (7); dashed lines) with those calculated according to Eq. (A.4) for WCZ models A–H of Paper I (grey area bounded by models E and D). Bottom panels compare the same models, but calculated throughout the neutral zone only (this paper: Eq. (13), solid black line; WCZ models of Paper I: Eq. (A.5), coloured lines).