  We study the minimizers of the fusion frame potential in the case that both
the weights and the dimensions of the subspaces are fixed and not necessarily
equal. Using a concept of irregularity we provide a description of the local
(that are also global) minimizers which projections are eigenoperators of the
fusion frame operator. This result will be related to the existence of tight
fusion frames. In this way we generalize results known for the classical vector
frame potential.
