Optical to X-ray flux ratios and X-ray luminosities for the 38 sources with a firm classification as per our methodology outlined in Sect. 2.4. We plot the different classes as: star - red circle; XRB - grey cross; YSO - purple triangle; CV - cyan cross; magnetar candidate blue pentagon; γ-Cas star – green diamond. Note that the apparent linear trend for some YSO, CV, and XRB sources is due to the lack of a MW counterpart with an associated distance estimate, or the lack of any MW counterpart. In these cases we use a distance of 8 kpc in deriving a luminosity estimate and the Gaia detection limit as an upper limit for the optical flux. Sources without a distance estimate from a MW counterpart are shown as un-filled symbols.