Neon dotty's can be aggressive enough to stand up for themselves but they are also able to dish it out on fish that are similar to it, ie hang around the rock work and are long and slender. I would say your sixline is the problem as it would be the most likely aggressor and the most likely to get picked on should it currently be peaceful (they generally mature into beautiful but nasty little wrasse and that coming from someone who loves them).
I bred neons years ago and they were really rough on each other and had the potential to be nasty. I had others that were really docile as well but I'd generally suggest them for a tank with tank mates that can handle themselves. If you moved on the sixline it might be a nice addition but could give the odd chase to the damsel.