Welcome!
Can't answer any of your specific questions with any real knowledge.
In SH3 - they seemed to understand your depth - e.g., if they were pinging you they had accurate depth information and would drop the DCs accordingly. In SH4, I don't know - I just started with SH4 because previously I had hardware poverty, and well, now that I'm eating Pacific swill I'm dying to be depth-charged. But my general sense, both historically and based on the simulation we have, is that the japs were hopeless at Anti Submarine Warfare (ASW). Which makes it a bit of a turkey shoot. But yea, look dude - you _want_ to be depth-charged right? You _want_ to have that Das Boot experience (though i guess it's a 'the boat' experience in the pacifiic). Anyway, chin up and be happy that something blew up very close to you.
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