I had the impression that casualties caused by missle fire seem to recover better than casualties from close combat. But that turned out to be wrong. It seems to be related to the class of the unit that suffered from casualties, not the one that caused them.

Because light and skirmish units are more likely to suffer from ranged fire you'll get the impression that it is the other way round, but after using Velites excessivly in melee I can say that has nothing to do with the kind of casualty. What I don't know is how it is acutaly calculated: only by the class of the unit per EDU or by their armour level?