MRV...
Generally speaking, I go after a convoy where the plot to intercept is always ahead. I don't bother with fast task forces, or convoys where I have to "chase".
If you're going to intercept ahead of the line, you'll have the luxury to set up whereever you choose at a 90 AoB and wait it out for however long or short it takes. I have found though, the longer you have to wait the odds increase that the convoy will change its bearing and there you sit...!
