Wouldn't I get more battery life if I was using a 1.8 Ohm head at 3.2 V, rather than 2.5 Ohm at 4 V?
Battery life is not a problem because I only charge it once every two days. This battery is a beast (or I am a wimp Vaper).
Hmmm.
You should try it and let us know!
Basically, you're pulling less watts at the 1.8/3.2 than the 2.5/4.0 so I would guess so.
However, we have to question that simple calc due to buck/boot converters in VV mods. The buck (cutting voltage down) MAY MAY MAY be more efficient than the boost (pumping voltage up by drawing even MORE amps than you think). My guess is that it just bumps all the voltage up to 4.8 and then bucks it back down to whatever setting it's on. Maybe it all comes out in the wash and the watts calc more-or-less works.
I'd be curious as to what people have found out.
Besides...a "mummy" should have plenty of time for these R&D projects!
EDIT:
(In reference to question #1)
If the manufacturer and/or vendor is cautioning against it.... maybe ask them why. I suspect it's because someone will turn up the voltage to max and run a 1.5 ohm coil or something and fry the e-cig. 1.5 ohm DCC's at max volts for example.
I'm guessing 1.8Ω at 3.2v is OK. But check with the vendor/manufacturer...not my advice. The other thing is that if you ever mess up and run it at max volts with less than 2.0 ohms accidentally....it could fry the circuits...so 2.0 is a safety thing by either the vendor or the manufacturer. IDK...do you have a link to the caution?