Small stone walls ones are easier to defend. Especially in some coastal cities (Alexandreia comes to mind), where playing out a battle is just waiting for the archers and slingers to kill the entire army, because of the "walking" through hostile missile fire issue. I think that is a part of the v1.0 bugs that was not fully quenched.

Sally defence = instant death to the attacker then. It does not work as well with the bigger stone walls. As cheap as it sounds, it is actually a useful way of getting rid of unrealistic amount of unit stacks, especially when such amounts of units cannot be justified (i.e. when you have control over the area for 20+ years, and Ptolemaic control of their heartlands is non-existent).