When your units are stacked, either in a town or out of town. When they are attacked, the strongest unit relative to the attacker will be chosen to defend. This will often mean that a highly promoted unit will have to fight. Doesn't this mean that your most experienced units sometimes will fight first and die, if the attacker is strong? When what you would wish is that your weaker units take the first blows and the experienced ones will live to fight another day. And let designated defenders with city defense do what they are supposed to do. And let units with city attack promotion attack cities. Even if they are a little bit stronger. Cost of unit production also matters. How do you deal with this - if you want your elite units to survive? Does this make any sense?