Despite your lack of experience Lt. you have very astutely come to much the same conclusion as myself and the good Captain Kiwi. We can only assume the position that the guns themselves in their revetments were taken down or damaged thus causing the rapid decline in fire power.
Luck seemed to play a part in both trials re the attrition of men as it is often the ships which take more damage than crew in most of our games unless a boarding action or close action with grapeshot is involved.
All the action in our game was at long range and thus used only A damage chits.
No heated shot was employed at the fort as there is no evidence to suggest its use in the actual battle.
Rob.