Dependence of the total multiplicity fraction of systems with q > 0.6 on the number of selected main sequence members of each OC. OCs with extended low-mass main sequences (m_min < 0.6 M_⊙) are highlighted as big orange circles with errorbars. The names of the two OCs with extended low-mass main sequences and high (and thus possible candidates for close-to-disruption OCs) are annotated.