Predicted vs. observed length of the bright phase (FWHM) for a column on the white dwarf at a latitude of 68° and an azimuth of 18° as a function of its height. The height is given in units of white-dwarf radii. The chosen inclination is $87\stackrel{°}{.}4$. The dashed horizontal lines illustrate the observed lengths of the four fully covered bright phases on 14 May (magenta), 15 May (blue), and 16 May (black).