I've got a couple of different coils set up with 1.5mm and 2mm "flavor" wicks. Both seem to be working quite well with 80/20 and 60/40 juices. On both, I've experienced no leakers, dry hits, burned hits or gurgles. I also have both set up with flipped coil seals. YMMV.
Yes, I am referring to the two loose wicks that you can easily remove. I do not know how much of a difference these wicks make, however, when I removed them from my heads, I neither noticed an improvement or a decrease in quality of the unit. They did however, improve the tight draw and muted taste in some of my coils. I suppose more good has come out of it, as nothing bad has happened as a result of this change. Of course, you can always replace the wicks and flip the silicone seal cup back to whichever way works better for you.
I would like to know of a good replacement for the wicks as well... just to see if it makes a big difference.
I personally removed both, but you can try removing one at a time and see if that makes a difference for you. Exposing the coil is a good way to clean it though!