Comparison between the H ionisation structure (red dashed line) and the Lyman continuum optical depth at λ ~ 900 Å (black solid line) versus the distance from the stellar photosphere. Solid lines are reserved for the wind optical depth, whilst the dotted horizontal lines indicate the transition between optically thick and thin part of the wind in the Lyman continuum (τ = 1). Red colour on the right-hand side is used for the H ionisation structure.