Regarding the OP, meh. Lightning sorties aiming to destroy the attacker's siege equipement and therefore factual ability to actually storm the fortress were very much par for the course historically. Heck, fortresses typically enough had purpose-built sally ports for the job, and canny defenders sometimes made holes in their own walls to mount a surprise attack... Granted they weren't usually done in the middle of an assault, but RTW sieges are somewhat abstract anyway.