Distributions of the 3D smallest normalised separation in real space between compact and galaxy groups (dark grey histograms). Each column represents a different subsample of CGs, each row represents a different GG subsample. Each panel also shows the distribution of the 3D smallest separation in real space among the GGs (black empty histogram). The light-grey region in each panel determines the inner region of a GG. Inside that region we quote the percentage of compact groups that are expected to lie inside a GG (see Sect. 3.1 for a more detailed description of each subsample).