I posted this on another thread, it may help:
Great, here is what I have observed watching on hundreds of SS wicks I have fiddled with and looked at under high magnification, with the juice on top you don't want a hole. When the coil heats up the juice boils and rises thru the hole back into the tank (pure physics), this can cause dry hit on a hard draw, also that rising juice ends up contaminating the juice in the tank. When you are off the trigger the juice flows like a straw down and it is very hard to control the amount and can very easily flood the atty. For me the best is a 2 to 2.5 mm dia wick rolled tight no hole and that takes about 45 to 50mm of 400 mesh and this way you get true wicking and no straw effect.. I have not tried any 320 yet. Now when your juice is under like the Line you benefit from a small hole and the heat rising effect on the juice like a volcano and I normally do 45mm around a small paper clip. As a test I made two small kerosene lanterns out of 5ml bottles one with 1mm ss wick and the other with a 2.5 mm wick, the small wick took 21 min to burn the 5ml of kerosene and the larger wick 3.5 min. I also did 2.5 wicks with different sizes of 400 mesh rolling them looser and the most efficient was the one I could get the most amount of mesh into the diameter.