Intresting technique, I will surely try it the next time I get a convoy under my hands (still in 1939, early war, second patrol).
I also think about a little variant of your technique: after you hide under the baffles and match course/speed with your cover ship, instead of navigating in this way for the next half and hour or so, slowly and steadly increse depth till near maximum depth while slowly decrese speed till silent running, eventualy going for all stop while listentning on hydrophone and waiting for the whole mess to go away...
