Area scaling factor (Equation B.5) as a function of source orientation, ϕ, and observer separation angle, θ, for two source semi-axis ratios, ρ = 0.5 (a) and ρ = 0.25 (b). The closer ρ is to 1 and the closer θ is to 90° the smaller the scaling factor, i.e. the closer the derived area is to the source area. The dashed green-yellow curves at 95.4° represent the separation angle of STIX and XRT relative to the flare X-ray source of SOL2021-05-07T18:43 M3.9.