Separation between X-ray position and the selected counterpart normalised by the one-dimensional positional error of the X-ray source as a function of its r-band magnitude for the sources with secure counterparts (CTP_quality ≥ 2). The hexagons are colour-coded linearly according to the counts in the specific bins. The marginal histograms have a linear y-axis. The 90th percentile of the r-band magnitude distribution (22.88) and the median of the normalised X-OIR separation (1.22) are also reported in the marginal histograms. The 1σ Rayleigh distribution expected for the normalised separations is overplotted in green.