No control of towers, stone towers etc

Following case:
AI Army comes in with knights on the front and some rams in the back against a stone wall + towers.
They are all in the fire radius of the towers but i was not able to order them to shoot just on the siege units. Is that intended or a bug?

Thank you!

Same issue with Keeps. Don’t appear to be able to direct fire. The keep just selects a close target and focuses fire.

Think this is intended as to let rams soak arrow fire etc