The assumption that the ionization and coagulation of metal plasma-generating cluster source can be described by the orbital limited motion theory, when it was examined by Monte Carlo calculations, was found inadequate. That assumption cannot firstly predict the modes of cluster ionization observed experimentally. Secondly, the effectiveness of coagulation was found to depend on the initial size of the condensing particles. Specifically, the coagulation of dust particles proceeds in a satisfactory degree. The coagulation of single atoms in a cluster source, however, saturates at about 140 atoms per cluster, in serious underestimation of relevant experimental data.