The best way to evade escorts is to avoid them.
I'll track a convoy for as long as it takes to get in as good a firing position as possible, night, bad weather, etc. I set up at 2800 yards or more at a 70° attack angle if I can. Depends on which firing solution I'm using, TDC/PK or a zero gyro angle Okane or vector analysis.
If I'm using my bow tubes as soon as I fire the last one I go to full power astern and set depth to 300 feet or so. I'll back out for as long as I can and when the escorts get close cut to 3 knots, silent running and throw in about 15° rudder. This way you seem to get farther away from your firing position and still keep a low profile to the escorts. Haven't heard a close depth charge this whole career.
Torpx is dead on about the flank speed timing thing. It takes some practice but can be done.
I will wait 30 or so seconds after they pass and cut to 1 knot and go to 15° rudder as well, you'll coast farther that way.
Magic