destroyer detection range and how-to-destroy...

[Manucubus]

cause i was sunk again quite recently, i restarted my career, so i am only at my 2nd patrol in 1939 now...but i already have sunk my 2nd destroyer. Let me explain:

1st patrol, east of scotland: approaching a destroyer perpendicular to his course at flank speed, submerged (yea, i know, but 1st patrol, so who cares if i die?), he did hear me, speeded up and turned towards me. I turned towards him, waited until he is only 1000m away and fired all 4(!) bow fish on him. Three of him hit and he sunk like a stone (prob i blew away half of the ship).
Question1: i always thought that the impact pistols need an angle of 90 +- 20 degree? So i didnt expect a success rate of 75% when firing at his bow from close distance? Is it always the case? Do i have good chances to sink a destroyer with by aft torpedo while running away from him? Also in the late years of the war?

2nd patrol, north of scotland: night, spotted a destroyer at long distance, periscope depth, destroyers course brings him _very_ close to me. Silent running, 2knots, getting myself in position, fired 2 eels on his broadside at distance of 700m. Both hit, blubbbbbb, destroyer is past. My stealthmeter was always green and my victim didnt notice me at all.
Question2: What is the detection range of a destroyer if you are silent running at 2knots perpendicular to his course? Can you also approach to less than 1000m without being detected in the late years of war (if he doesnt suspect anything)?


i am playing GWX 76% realistic or so (just let the computer do the firing solution and map update) and only the 16k mod

thx for reading