Angle η between the jet axis and the line of sight at the epochs of the VLBA runs A-J. The trend of η vs. Φ(P₁) is shown together with the VLBA maps (Massi et al. 2012) (see Sect. 4.5). The VLBA runs cover 30 days, then more than one orbital cycle of 26.49 days; runs I at Φ = 0.203 and J at Φ = 0.316 were performed one cycle later than runs A at Φ = 0.187 and B at Φ = 0.30. The shift of η (corresponding to a shift of the maximum Doppler boosting) is already appreciable in Fig. 7 even after just one P₁ cycle; i.e., the two η curves (black and red ones) vs. Φ do not overlap.