Main rulebook, Fighting combat, starts page 68. Last paragraph on page 69 deals with fighting to the flank or rear. “Whatever its situation, a unit cannot allocate more than half its attacks to either flank or rear.”
I would say yes, it is an initiative order and for that you need to be within 12″. It may not get you out of range of the enemy but it does leave a space for you to move fresh troops into.
