Welcome, Althar93.
The only issues/FUBARs that I've encountered regarding unusual ship sinking mechanics is when I have a screwed-pooch game load and as of yet, I haven't been able to nail down the exact cause for those bad loads. I can speculate that it had something to do with high TC (time compression) or, in my particular case, I like to experiment using the same scenarios over and over in a (What if I did this?) semblance of a science-like control group thingy.
Basically translated, I do some weird stuff with reloaded games that may account for ships failing to register as "sunk" in my Captains log and whatnot. In the end, a simple reload of the saved game usually cures the problem.
As far as approaching/evading DDs, in my own experience, as
nerfed as it may be (
Armistead uses that word alot, I like it too so I'm using it also), I find that if your screws are facing away from the DD, it makes you harder (not impossible) to detect.
Also, look at this picture-type, schematic, reference, visual aid like thing below:
You'll find this on your periscope screen. If you are in the DDs baffles (Dead Zone), he cannot hear you. This thing shows your position relative to the target angle.
BTW, if PE4 is referring to Pacific Environment, that may be the cause for your nerfed ship sinkings. The major Mods (TMO, RFB) already come with their own environments and aren't too friendly toward additional ones.