Actually they have flank bonus.
Light Cavalry - 30%
Heavy - 20%
Paladins/Cataphracts - 10%
Cavalry Archers - 50%
Cataphract archers - 20%
Wait a sec. I think tiger told us that they don't have flank. Now we have formation flank and i did some calculations. Putting army on flank, most of the time, is not smart thing to do.
When you go against ballanced formation most of the time you lose more than if you go with balanced formation. If they really do have flank bonus than i should lose less and not more because cavalry would kill flanks faster and than focus on center.
I would do more calculations and confirm or deny what i just wrote.
Ahh yes, I did calculations against real players armies when i was getting ready to attack. Not once i activated any other formation than balanced because i always had higher army loss