Illustrative comparison of 1RXS (yellow boxes) and 2RXS detections (green circles) for the field 930 304. The image shows the intensity distribution in counts. Perpendicular to the scan directions the count rate shows intensity variations. At the intensity peaks many 1RXS detections do not have an 2RXS counterpart. As the detection algorithm for the 1RXS sources is run on a much larger field size (6.4° by 6.4°), the background at the intensity peaks is often underestimated and the detection likelihood of the sources is overestimated. For the 2RXS sources the detection is run on nine subfields. With this the detection algorithm can much better follow the count rate variations and the background is determined more precisely. At the intensity peaks the background is higher for 2RXS sources and fewer 2RXS sources are detected than at 1RXS. With the white crosses we show 2RXS detections down to likelihood values of 5.5. Some of the 1RXS detections do have an 2RXS counterpart when the likelihood is decreased to 5.5.