Resistance of the coil? I used to (and still do) vape on my Provari frequently at 3.4v if that's what it takes to get the taste I want. When I bought the Segelei Zmax V3 I started vaping at 6w. Sometimes, I'd get down to 5.5w.
Wicking can be an issue with any atomizer. With a top coil, the juice around the coil can gravitate back down the wicks when you set it down. There can also be restriction where the wicks enter the head and that limits the juice feed.
If it's a dry coil, try taking a few dry hits then press the fire button. Lay it on its side when you aren't vaping to let the wicks soak. Turn it from time to time to let the other wicks soak. Most Vivi Nova users are tank turners for that reason.
If all that doesn't work, you might want to try some bottom coil tanks. Kanger Protank or their T3, T3S, or Evod might just be what you are looking for. The coil sits at the bottom of the tank and feeds much more reliably.