No expert myself, but I really don't think it should matter one way or the other. You should (theoretically) get the same gains either way.
Maybe being on the server line reduces the risk of water elementals/sea serpents bothering you? Doesn't make much sense to me, either, though--I always went slow forward while fishing, and none of the kept up, they'd fall in line and eventually get left behind--assuming I'd found a line that was unblocked by other boats.
(Related note--how many boats are still out there? Used to be thick, but I can't imagine it being that crowded anymore....)