Manual torpedo's. Help me!

[Bakkels]

Ok, so after a couple of hours of playing SH3, I'm already bored with the auto-aim. (I'm really getting in to the whole realism-mojo already ) So I tried manual targeting.. And it's almost like SH3 anticipated this, because on this patrol I stumble upon two lonely, small and slow merchant ships. Ideal target practice.
However, all my torpedo's missed of course As I tried following some of them with the free camera, I saw most of them miss a couple of meters off the stern. So another couple of noob questions arose:

- First, what is the point of determining AoB? What I mean by that is, you
typically only fire when you're pointing at the target ie when the gyroangle is as close to 0 as possible. And you try to fire at a 90 degree angle with the target's bearing. Then your AoB should also always be close to 90 degrees right? Then why determine AoB? Clearly, I'm clueless

- Second, timing. The GWX manual says to start with inputting range in the
notepad. Then AoB, and finally speed. But measuring speed takes 15
seconds (or 30 when you're trying to be more accurate). By then
range and AoB are completely off. Again, what am I missing here?

- Finally, when firing your torpedo, does it make a difference at what height
you aim your periscope / UZO?

Thanks again!