so apparently it "varies" (pun?)... from unit / atty ...
imo, that's not an issue... one definitely has choices of sweet spot/ atty combinations to satisfy majority of tastes.
Every atty vendor i've seen says not to use higher voltage than what a "3.7"
device will provide, so Provape is in the conventional ranges. The point is that with the Vari, you have a wide choice of resistance to voltage...to suit the majority of vapers.
i prefer reg. 2.2-ish Ohm attys at anywhere from 3.6 to 4.5v depending on the atty and how abused or fresh it is. (my favorite is a DSE 901 2.8 - 3.0 Ohm at those voltages).
Granted, a 4.5 or higher Ohm HV atty is not a great idea if you like your vapes pushing to the max. It won't get it at those upper ranges... nor at the lower ranges (LR). Not an issue for me.