Representations of the model geometry. In panel a we see the model as viewed along the y-axis. In panel b the same figure is seen from “over the shoulder” of the observer. The jet direction J is shown as a red arrow, the jet angle θ_j this makes with the x-axis is also shown. The distance d_o from the observer to the jet along the x axis is shown. The Blue arrow skimming the jet’s upper surface indicates the maximum angle subtended by the jet to the viewer θ_m. A black line, representing the direction of photon observation, pierces the cylinder surface at s₁ and s₂ subtends an angle θ <  θ_m. The second blue arrow indicates the maximum (in magnitude) ϕ angle −ϕ_m subtended by the viewer and the jet’s side edge, as indicated in panel b. Also shown in panel b as a dotted line is the projection of the photon observation direction into the x-y plane and the angle ϕ which indicates its off-set from the jet’s central axis.