IMHO, you should try to take a 90º angle possition, pick the juiciest targets form long distances, fire your eels and dive deep and move ahead of the convoy in paralell, that might give you the chance of reloading and making a 2nd attempt.
if you are at a good distance, if you dive as soon as you fire your torps, escorts might not even detect you. If they do, you have more than enough distance to run away completely safe.
I hope it helps you.
CapZap