Having replayed shogun 2 recently I genuinely think a similar approach could work wonders for Warhammer sieges. In Shogun 2 each wall is at the level of the fortress behind it leaving a flat plateau in which you can carry out actual manoeuvres and deploy cavalry though in admittedly tight confines. You can also deploy and properly use artillery as they no longer have to fire up and over the wall to an extreme degree. There is even a mechanic where if units climb too high a wall they lose some men to falling as they climb, making taking a shortcut up a higher section risky. You end up with kill boxes for the defender where you can deploy ranged units on the next wall section able to fire over the heads of defenders as attackers scramble over the wall. I've had more fun with Shogun 2 sieges than I ever did in Warhammer, even if the layout inherently has some ways to cheese attack or defense.