I've found the Cellucotton reasonably consistent, but I absolutely compress the majority of it before wicking. Take a 2" piece, cut it in half. Start compressing maybe 1-1/2" of it. Unlike cotton, where I've read to only twist in one direction, it seems to be fine to twirl rayon back and forth to get it to compress. Clip off fine strands at the main end before inserting into the coil If it does bunch up a bit, pull it back a little and re-compress that part. Don't forget -- when pulling through the coil, it should be quite snug but not actually deform the coil.
On the Aromamizer, for dual vertical coils I rewick in place, clipping off about 1/2 the tail and using the remaining strands to cover the 2 eliquid ports on a given side. For a single vertical, coil between the posts, I end up popping out the coil and rewicking, then reinstall the wicked coil -- a bit of a PITA otherwise, trying to fish half the tail to one side, the other half to the other, to cover all 4 eliquid ports. I don't bother thinning the tail for the single vertical -- in theory I should thin each half, but I tend to over-cut if I do.