Yeah...I getcha..
I'm a mesh virgin but just looking at it I figured that 400-500 would wick better than 250-270?...
I get cappilary action...
Yup. The closer the mesh strands are (the higher the number) the better it pulls the liquid up. The further they are, the better the liquid travels down (for top-feeding tanks). The trick is to roll as much mesh as you can, as tight as you can, so that it is snug in the wick hole (but not to the point of forcing it in there.)
....that and 33mg Nic..