When is the top armor value used?
When is the (usually very weak) top armor value of a unit used?
Do helicopters always hit the top armor, or only when they are close enough to the target?
Can (non-artillery) ground units hit the top armor of units below when they are on an elevated position?
Solution 1:
Top armor provides protection against direct hits of artillery shells and (in AirLand Battle and Red Dragon) against all weaponry of ground attack aircrafts (guns, guided and unguided aerial bombs, missiles, rockets).