KAM - I've had a few more walled battles now and it's working much better. Perhaps it's because I use my units a lot more delicately when on the walls. But good stuff.
Also my other issue was massive friendly fire casualties. This has gone down a lot since I changed tactics, my peltasts only throw from behind/side of engaged troops. The looping ark tends to overthrow and destroy the wrong unit if positioned behind the enemy line. Also the faster battles have helped!!
SO all is good