Sample of extended (left panel) and compact (right panel) X-ray groups (black points). All optical groups are shown with grey points in both panels. Completeness limits for the FoF groups are shown in red (10%) and orange (50% completeness) dashed lines, and for the X-ray groups in dark blue (10%) and light blue (50%) solid lines. Systems below the 10% X-ray completeness limit are removed from the catalogues. We applied the same extended source cleaning to all catalogues used in the analysis.