The manual :
When both sides in a battle are finished firing there is a retreat check. On the Western and Italian fronts, if the defender takes 50% more casualties than the attacker he is forced to retreat. On the other fronts, if the defender takes more casualties than the attacker then he is forced to retreat.
The defender is also forced to retreat if at the conclusion of the battle the remaining attackers far outnumber the defenders as modified by the strength of any entrenchments.
Besides the forced retreat above, corps will also retreat individually from a hex if their strength or readiness fall to 0.
See screenshot. No way defender took 50% more casualties then attacker. If the Italian front now works like the East front it is IMO a huge mistake as mobility wasn’t a feature of that front.

