BP1,BP2 and IP: Orbital-phase evolution of the centroids of BP1, BP2, and the IP as a function of MJD epoch. The abscissa values correspond to the mean MJD across each bin (see Table 2). The dashed red lines are the best linear fits to the data; the slope and reduced chi-squared of each fit is shown in the legend. ⟨BP1+BP2⟩: The average orbital-phase shift of the centroids of BP1 and BP2 as a function of MJD epoch; the best linear fit is shown with a dashed red line.