Ive had a different experience with 6 line wrasse, I think I just got really lucky or I cant remember if I added him last, but I had 2 clowns and 1 6 line wrasse in a 10 gallon, this was when I was just starting out so i didnt know much the fish store had recommended me a 6 line, anyway i never had any issues they lived together very well for about a year and then eventually I upgraded to a 30 gallon, never had issues idk i think i got lucky, but being that you also have a pipefish I would agree with everyone about competing for food and id be more concerned about that as opposed to the agression espically if you get a small six line, same size as your other fish or even smaller.