The present work concerns the study of high-energy structures in the photoionization of Mg and Be metallocenes due to photoelectron diffraction. The influence of geometrical structure is studied by varying the metal-ring distance in MgCp2, as well as that in the permethylated compounds MgCp2* and BeCp2*. The cross section ratios relative to the two outermost valence ionizations have been studied and found to be very sensitive to the value of the metal-ring distance and to be able to resolve ambiguities in present experimental values. Further differences are attributed to minor changes in the electronic structure. The results confirm that long-range oscillations in molecular photoemission cross sections constitute a general phenomenon and are an easily measurable observable that can be used to obtain important information on the geometric and electronic structure of the target.