So, if you load an army with all units the same type and supposing those units are 6/3/3 (i.e. Cavalry) then:
Attack bonus with:
Neither Pentagon nor Military Academy: (6+6+6)/6 = +3
Pentagon only: (6+6+6+6)/6 = +4
Military Academy only: (6+6+6)/4 = +4 (rounded down)
Both Pentagon and Military Academy: (6+6+6+6)/4 = +6
With Pentagon and Military Academy, assuming you load 4 units of the same type into each army, the net result is to simply double their attack and defense stats, because the bonus is (4*X)/4 = +X Which makes a 4-Cavalry army into a 12/6/4 unit.