IF the design was done right, the difference between the two batteries should not make a difference, other than battery life
although some mods in the past needed the 2 batteries to provide you with the full range of settings.
I can't remember which ones, I seem to be recalling the evo? might have been one.
The reason for this is the type of circuit, or better yet the type of chip they used to give you the VV.
With a stacked battery configuration being the deciding factor, one would assume they are using a buck converter, which takes the high voltage and drops it down. So if 2 batteries were needed, and the max voltage was 6V's they internally with some electronic bits and pieces they chopped the voltage to 6 V , as stacked batteries would be 7-8 off the charger.
Then as you decreased your voltage with the buck you get lower voltages, and high voltages meant they are just now lowering as much any more.
In the case of something like the Provari or zmax that uses either a single battery or dual battery and can provide you with the same range ( on paper ) then it is probably a buck/Boost ( more voltage than the battery is ) regulator that can do either depending on the voltage available.
The difference is the drain on the battery.
So it isn't the voltage from the battery that determines the wattage but the regulator ( buck/boost ) which will increase or decrease the available voltage based on your settings and of course the resistance that provides the current.
Might be hard to believe but I tried to keep that short and sweet lol
