Be careful with 3mm. It just might be too big of a coil for RTAs, with a dripper it's another matter. 3mm coil will pull in (and hold) more juice vis-a-vis the atomizing capability of the atty. And that could be prone to leaking.
Qorax...
I'm currently using a 2.8mm micro coil, with absolutely ZERO issues...and can't imagine 0.2mm making that much more of a difference...
I think the key to running a coil that large in diameter is how high you run the voltage/wattage.
I'm running it at 10 watts, it's a 28g 5-6 wrap 1.4 ohm coil.
Japanese cotton. The thing wicks like a dream. Not that 10 watts is high...but maybe it's the threshold?
Junny, I have a question for you...
Are you making sure to close your juice control, immediately after you put the tank back on?
The way I do mine:
1. Turn KF4 upside down
2. Open JC
3. Unscrew tank
4. Build
5. Turn KF4 upside down
6. Attach tank
7. Close JC
8. Turn KF4 right side up
9. Open top cap
10. Fill
11. Close top cap
12. Open JC