[shinyhalo]

Melee units retaliate immediately when attacked by Melee units.

Melee units don't retaliate when attacked by Skirmish units or Archery units because the attackers are using ranged attacks then, presumably, retreating.

Skirmish units retaliate immediately when attacked by Skirmish units because both have equal range weapons.

It seems to me that, realistically, Archery units would be able to retaliate immediately at Archery units and Skirmish units since they can attack at range.

I don't know how to Mod this, but since Skirmish units can retaliate against Skirmish units, it should be possible.