Attack unit located in a river hex

[Guardian]

If I understand correctly, unit A has normal statistics, while unit B, being on a river hex has severe penalty to its defence (unless it has some river-friendly perks). When unit B retaliates nothing really changes, B still has defence penalty, not attack, so it will attack with normal strength, but when unit A retaliate it will inflict more damage, because unit B is still on the river hex and still has negative modifiers to defence.

..Unless that how it worked in Fantasy General and works here for me atm, if anyone knows better please share Your knowledge :]