Mass-spectral results on alkali clusters containing one host-atom with ns(2) valence-shell configuration (Mg, Ca, Sr, Ba, Zn, Eu, and Yb) are presented. They allow uncoupling of the number of atoms in the cluster from the number of its valence electrons by probing with elements with more than one valence electron and different ionization potential and atomic radius. Prominent intensity maxima for specific cluster sizes are observed. Based on an electronic shell model, a systematic interpretation of the intensity maxima as a function of the incorporated heteroatom is presented. Although most of the gross features can be rationalized within a purely electronic model, a more refined analysis prompts one to geometric structure-effects which have to be included to more fully describe the spectra.