Yep. It's most definitely the coil resistance. 7V on a 1.6-ohm coil is 30W. With a higher resistance coil, you can go to 8V, but keep in mind, the iStick 30W is really a VW mod instead of a VV. It has voltage control, but the wattage is what is regulated. The voltage adjustment mode will only allow for the equivalent voltage of 5W-30W.