Contrary to previous results concluding that all 7 X 7 boundaries in the down step edge were complete, 5 X 5 faulted half units were found to be introduced in part when the transition region was narrow. In addition, the formation characteristic of the 5 X 5 faulted half units was strongly influenced by the type of step configuration (nF or nU) and by the structure of the upper step edge (complete or incomplete). Even when the step configuration was the same, the difference in the upper step edge structures strongly affected introduction of 5 X 5 units.