When I readed the post title I thought you were referring to a situation where you find your target with zero AOB, i.e. coming directly at you. This is a great situation because you have a very easy shot. The target course is perfectly known to you, and by heading towards him (On a head-on collision, so to speak) you can determine his speed quite easily by seeing the mast grow in the reticle.
I love to attack like that by getting close and then heading 90º left or right to make some distance, because by doing that I know that I'm exactly at right angles to the target's track and have a very, very easy shot. I can simply point my periscope some degrees towards the target for the perfect zero GA shot, as you suggest.
That's also one of the reasons I love the Salmon/Sargo and their 4 rear tubes
