Definition of angles and conventions used in this paper. Throughout this paper, we adopt the ‘observer’s convention’ for all geometric quantities. The fundamental reference plane is in green, and the orbital plane is in purple, with the corresponding unit vectors coloured the same way. S denotes the spin angular momentum, which is aligned with the orbital angular momentum. The magnetic axis (μ) is misaligned from S by the misalignment angle α. The pulsar emission cone has an opening angle ρ, and is cut through by our line of sight at an impact angle β. ζ = α + β is the latitude of the spin axis, which is the same as the orbital inclination angle (i) for spin-aligned systems.