Top left: spectral line of the reference model (blue), seen from an inclination angle of 0 degree (face-on). Overplotted is the spectral line of an exclusively homogeneous spherical outflow with identical global characteristics. Top right: wide-slit PV diagram of the reference model. The linear colour map at the bottom provides a reference to the colour coding. Every coloured diagram is constructed using this map. MAX represents the maximum emission in the PV diagram.