Are you using rayon? I don't have any trouble at all with Japanese cotton. I use a pretty large ID, between 2.8mm and 3mm, so I use two pieces of cotton then I twist the two end together tightly and it slides right in. In my experience if the wick is even just a little too tight I won't get the flavor I want so I've got it down to a science now. I take one pad of cotton, i rip the two outside layers off then cut two strips off.
I don't want to rewick my build yet so that's as far as I want to go. I hope that helps you, I really have no problems at all building or wicking with ni200. If your using rayon than that's a different story, I prefer Japanese cotton but I do use a similar method for rayon, it is a little bit harder because you want rayon tighter than cotton because it doesn't expand like cotton.