im almost 100% positive the game "cheats" on its depth settings. When the AI does acutaly attack, it rarely misses with its default settings. Infact, when depth charges are dropped, i acutaly go deeper to get away from that depth. Assuming that the depth charges are "set" at whatever depth i was when they were first launched.
Of course, those depth charges still seem to manage to explode close, regardless of depth change