Schematic representation of the geometry involved in the absorption point displacement due to reconstruction errors. Here, P_src is the location of the point source whence the photon come from; P_i is the true impact (absorption) point of the photon, displaced due to the mirror PSF, while the orange double-headed arrow represents the photo-electron direction, n; P_r is the reconstructed impact point displaced by an amount δx along the photo-electron direction plane. Then x−y are coordinate axes chosen such that x is parallel to the photo-electron direction plane, while ∆ϕ is the polar angle of the reconstructed impact point in the same reference frame, describing the azimuthal distribution of photons due to the mirror PSF.