A phalangitai unit has shield value of 5 and this alone requires an attack value of 11 to just pass through that defence bonus. Now take into account the aditonal armor of at least 4 ( 8 :2 for sling ) and try to kill any of those guys with an unexperienced slinger from the front with a value of, say, 2 or 3 :) A slinger unit must then have an attack value of 15 to cause any significant damage on a phalanx unit from the front, which is not possible in EB without tweaking the EDU.
I also do remember reading, that defence skill only applies to the front and the right side, but shield and armor are there for instead. But while attacking a unit from the rear, some soldiers always would turn around and fight back.