Pretty much, you want a solid barrier between the juice and the outside. The only place it should be touching something other than metal, o-ring, or glass, is the cotton. most of the times, there's NOT a gasket or o-ring where there's threading, but if I can, I add an o-ring there if possible.
So if there's only one way for the juice to go, it HAS to go through the cotton. That leaves you with the amount of cotton to determine the amount of juice that flows to the coil. Less cotton means less resistance for the juice to flow to the coil... too little, and it won't offer enough resistance to keep the coil from flooding. On the opposite end of the spectrum, too much cotton won't let enough juice to get to the coil fast enough, and you will end up with dry hits, and possibly burning the cotton the coil is wrapped around. That's called a dry hit, and it's not very pleasant.
That's the basics of how most tank atomizers work. You should've seen the times leading up to this setup... for a while, it was where they had a reservoir, and the juice had to wick up to the coil.... but.. if you turned the atomizer upsidown, juice would leak out like crazy. Other methods are just to keep all the juice in the cotton.. that's how most of the "cigalikes" nowadays work... but since they hold so little juice, the atomizer has to be tiny or it will burn up all the juice in one or two puffs.
