Evolution of the impact angle β in one precession cycle for the putative companion pulsar for different magnetic inclination angles α and spin-orbit angles δ (0°, 5°, 20°, 50°, and 90°). In panel (a), α = 0°, in panel (b), the angle is 45°, and in panel (c), it is 90°. For panels (a) and (b), β_MP and β_IP are plotted using solid and dashed lines, respectively; for panel (c), the β_MP and β_IP curves coincide. The invisible β regions are filled with gray shadow. Since the reference precessional orbital phase Φ₀ of the companion is unknown, the reference MJD₀ is chosen to be the epoch that Φ₀ = 0°. For reference, a scale bar that shows the observing duration of PSR J1906+0746 (∼7000 days) is plotted at the bottom of panel (a). This span can occur anywhere in the cycle.