Not-to-scale schematic of the geometry of the spin-orbit resonance model with an active phase window. The white dwarf is shown in light blue. The orbit of the companion is shown by the outer black circle, with the orbital phases corresponding to integer numbers of white dwarf rotations labelled. The cross shows the location of the magnetic axis at a white dwarf rotation phase of zero. The black dashed lines indicate the magnetic field lines connecting the white dwarf and the companion at the corresponding orbital phases, with the blue circles on the white dwarf showing the location of the footpoints of these field lines. The active phase window is shown as a shaded region along the companion orbit.