Interesting thread.
I use similar tactics to herr kaleun Schöneboom and most of the time it works although I always find the targeting period nerve-wracking. I played a late war single mission recently (the rendezvous with a small trawler) where you are up against a HUGE convoy with many escorts and I did manage to sink a medium tanker and a large freighter and thought I had escaped the destroyers and corvettes but I hadn't counted on the trailing HK group.
I left my bedroom briefly and when I returned I heard the terrifying sound of being pinged. I raised my periscope and was horrified to see a destroyer bearing down on me. I froze initially, contemplated a dodgy stern shot but then realized I was in mortal danger and tried to crash dive but got caught in a series of close explosions which tore the sub apart.
Stupid kaleun!