This is something that requires some experimentation. Everybody has their own opinion about it. Some folks like solid wicks, with no center hole. Others like 'straw' wicks. Some like the wick to be fairly snug in the wick hole. Others like a bit of space around the wick. Some folks roll wicks bone crushingly tight. Some roll loose.
In general, the more mesh you use, the more
juice it will hold, but the more of a heat sink it will be. Meaning that more power will be required in order to vaporize the
juice.
A lot of it depends on the gauge of the mesh you're using, the PG/VG make up of the juice you're using, and the type of device you're using.
Just my personal preference, with the ZAP, I use about 75-80 mm wide, 400 mesh, rolled to about 7/64 diameter. Height is trimmed to the same height as the top of the center post screw. I can't answer about an iHybrid.