Posterior distribution for the pair of parameters (δ₁ and δ₂) introduced in Eq. (9), for the experiment using eRASS1-main as a test and eFEDS as a reference sample. The histograms represent the marginalised posterior distributions, with mean and 68% range overprinted. The contours represent the equivalent 0.5-, 1-, 1.5- and 2-σ distribution of the joint posterior. Clearly the parameter δ₂ departs from zero, indicating that a fraction of the systems we predict not be detected leak into the actual eRASS1 sample.