Schematic representation of the maximum coverage condition for an exemplifying case of non-central occultation geometry; here $f_{\mathrm{d}}=2$. Panel (a) shows in red the projection on the {x, y} sky plane of the X-ray source, whose centre is $C_{\mathrm{X}}$, whereas the projection of the occulting cloud is in black, with centre in C₀. In panel (b) the same configuration is seen from a different perspective, in which the line of sight to the observer is shown as the z-axis direction, along which X-ray photons are coming from the X-ray source from the left. See the main text for the meaning of other notation.