I agree with you, recently I attacked a convoy from 7 km away, and with no good visibility, so I worked up the data with the hydrophones (I use map contact updates). I shot 3 eels to different targets, and I got two hits. Another time I attacked a convoy from 4.5 km, with good visibility, 3 eels again, 1 hit one of the ships I aimed, another one hit a ship in the next row the one I aimed, and the third one missed. Escorts never knew were I was in neither of the attcaks
The trouble is that you need steam torpedoes and in good weather their trails are clearly visible, so ships begin to zig-zag (that was the cause of my second hit to an unintended target in the second attack). Maybe at night will be better.
So long, I have never reached year 41 so in 1940, when I am now, escape is easier than later, as everybody says so maybe it is not worthwhile an attack from such distances in this year but, ĦI am training for the future!