Some inaccuracies in Heroes of Might and Magic III½.

the damage dealt by towers, specifically during combat, depends on the strength of the monster being targeted: for example, if towers attack a low-level creature, the damage will be much higher than when hitting a high-level monster... the damage also depends on the spells cast on the target!))
and as already mentioned, the increase in damage depends on "time" - I won't repeat myself.