I have spent a few days vaping on my iStick, and no matter what, I still get the intermittent burnt hits. I keep it set as low as I can, and I have tried both voltage and wattage. It's not a wicking issue, as my juices are all 65/35 or 70/30 (pg/vg). It's not a resistance problem either, as I have tried coils that range between 2.0 to 2.9 ohms.
I have never had this problem my Twists, which are set at 3.6V no matter what the coil resistance is, and they hit perfectly every single time. My MVP is set slightly lower at 3.4V, as it does hit harder, but it still doesn't burn my juice outright. Setting the iStick to 3.4V or 3.6V is guaranteed burnt flavor.
It really feels like my iStick is faulty, and that the regulator is damaged. The burnt hits I am talking about aren't just a little burnt either. It literally tastes like the iStick is firing at the full 5.5V or 20W. It's awful!
Some Cloupor DNA30 clones and Fasttech delivered Hana clones have that precise impolite behaviour.... they do not regulate, they simply fire like a mechanical, no matter what you can toy on the buttonry and screen.... Obviously, they are faulty and as such, they've been returned...
I cannot recall now if you made some voltage measurements or not, but that would be the key diagnostic tool, if your iStick is performig in the same way.