The DNA-30 does not have "step down", so you may want to up the resistance of your coil a little.
I run my KF 3.1 at 9 watts. That would be 3.6v with a 1.5 ohm coil. .............. See the problem I would run into when the battery is still at 4.2v? I'd be at 11.75 watts instead of 9 watts.