MOST of the Iwo battles work just fine with the standard east - west retreat. There are always exceptions.
Switchable or selectable retreat paths have been on my "wants" list for quite awhile but by the time we do all the other things we need to do for release it always ends up an orphan on the "B" list. One of the foundations of the code is the units retreat toward "their" map edge and other additions to the game always eat up the time we would need to sort that out and ensure everything works
Don