4-34. In contiguous operations, the MBA extends from the FEBA to the rear boundary of a specific echelon’s subordinate units. Commanders locate subordinate unit boundaries along identifiable terrain features and extend them beyond the FLOT by establishing forward boundaries. Unit boundaries should not split avenues of approach or key terrain. Commanders select the MBA based on the products of the IPB process and their own analysis using the mission variables. The IPB anticipates how an enemy force will use the available avenues of approach.