A heuristic demonstration of blueshift formation in an axisymmetric, biconical wind. The left-hand panel shows the wind geometry for the fiducial model described in the text (model n), and the colour denotes the projected outflow velocity for an observer at θ_i = 15°. The right-hand panel shows the observed (synthetic) C iv λ1550 emission-line profile from a MCRT photoionization calculation using the same geometry, with and without an opaque mid-plane. With an opaque mid-plane, the receding wind cone is obscured and a clear blueshifted asymmetry is produced.