Relative distance (in units of the larger component R₂₀₀) between two component merging systems as a function of their virial radii ratio. Blue points indicate systems where both components contain at least 8 galaxies. The dashed line shows the merging criteria limit for our systems. Some of the smaller systems are above this limit, due to the poorly determined R₂₀₀ value, in which case we have also taken into account the size of the groups in the plane of the sky (see Sect. 3.3). The dotted line marks the R₂₀₀ for the larger component. For most of the systems the distance between them is larger than the estimated virial radius of the larger component.