In tactical battles for cities e.g. sieges, I think that watchtowers should provide a stationary building shooting arrows or the like with a low initiative. With battlements it could add some archers stationed away from the battlefield. Both the watch tower and the archers on the battlefielld should only be reached by ranged weapons, flying units (Varda), incorporal units (Banshee, unless the defenders has some kind of spiritual wall) or when all defenders on the battlefield has been vanquished. With all the defenders vanquished the attackers/besiegers could attack the door/gate.
if the attacker defeats the units on the battlefield and the watch tower/archers the siege is won.
It would also be nice to see siege engines e.g. ballista, javelin etc. which can target the watch tower or the battlements.
Another suggestion would be to make the battlefield "interactive" e.g. be able to destroy buildings, set fire to plants, bushes or trees. For example on tactical maps, where the middle is restricted due to a narrowing by plants, it could be possible to destroy the bushes to open a wider path.
Another suggestion is the Line of Sight.
I am aware this is a beta and that the engine and resources might set some limitations on the possibilities.