Orbital evolution of Hβ parameters obtained from the two-Gaussian model and a diagnostic diagram. They are all plotted against the orbital phase, and repeated over two orbits for visualisation purposes. Top panel: intensity ratio between the blue and red peak. The value deviating from the trend is in red. Middle panel: offset of the line centroid (black diamonds) and best fit from the double-peaked model (blue solid line). Bottom panel: offset of the line wings centroid (black diamonds) and best fit from the diagnostic diagram (blue solid line), corresponding to a peak-to-peak separation of a = 3800 kms⁻¹.