Geometry of the binary system and the jet in six objects in this sample. The plots show the system during superior conjunction, when the post-AGB star is directly behind the companion, as viewed by the observer. The plot in the upper-left panel shows the system viewed edge-on. The arrow gives the line of sight towards the observer. Right-hand-side panel: system viewed edge-on and during superior conjuction. Lower-left panel: binary system viewed pole-on. The different elements in the plots are the post-AGB star (orange circle), the location of the companion (orange star), the centre of mass (red cross), the jet axis (dashed black line) and inner jet edges (dotted white lines), and the Roche lobes (full black line).