AoB is the biggest one. If you scout out the Convoy ahead of time before dark then you will know the course and with the course you can easily calculate exact AoB. Also advanced scouting gives you accurate speed. With those two in hand range makes little difference so long as your approximation is in the same ballpark.
Also, when attacking a convoy using single torpedoes is not in keeping with realistic occurences. While Otto and the other early war aces would use the "one torpedo, one ship" policy, that was only when they could be in the midst of the convoy and fire at point blank range.
Mostly, however, kaleuns used spread shots to ensure multiple hits and sinkings. A spread shot is more forgiving for inaccurate solutions and it also has a good chance of hitting something behind the target if you miss.
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