Marginalised posterior distribution of the best-fit model of the X-ray plus optical selection function (see Eq. (15)). The filled 2D contours show the 1σ and 2σ confidence levels of the posteriors after convolution with the uniform priors. The green contours denote the base selection function where flux is measured within R_500c, the violet contours show the effect of measuring flux within an angular aperture of six arcminutes. The parameter values are reported in Table 2.