I'll play a little more with it. Right now I have 2 2.5mm coils in it and it's pretty good. Might try again with single to up the airflow a bit. The only single coil build I've ever done that was satisfactory to me was a single Z coil in a Stumpy on top of a regulated squonker and using temp control. Worked great.The folks in here have a lot more experience than me, but I kept trying different builds and found my sweet spot by moving up to a 3mm coil and lowering it a bit so I could see the bottom of the coil when I look in the air hole.