To answer about targets moving away. Theoretically, yes, with uber-accurate bearing lines it works also when the target is moving away and allready quite far. But since the bearing drift slows down as the target moves away it is difficult to get enough difference in bearing direction. Then the lines become more and more parallel as time moves on. Which is not good for this method. You also risk the target leaving your detection range. But you don't know when that is so don't let it stop you. Besides, Kuikeg developed a 4-bearing method that works when the uboat is moving. So, while on the surface you can usually use superior speed (full or flank) while doing it.
For practical use, ... well practise.
(And what TDW said)