Hey Shynobi the answer to your question is when dealing with volts (the 4.2), your coils are going to perform faster/better at the lower resistance (.2ohms), remember the .2ohms will require more amps, in other words using the higher resistance of 1.2ohms at the same 4.2 volts, it should be heating up much slower, because all that extra kanthal is absorbing/eating more power trying to heat up.
I think where you got a bit confused was the fact that you thought the lower res .2ohm setup required more
volts to get more wattage, which isn't true. In a nutshell, the
lower your resistance the
less volts you need to get to the same wattage. So it appeared that your lower res setup needed more power to perform well, when in reality it's just that the smaller coils need to be at higher watts to get the same performance as the larger coils, basically since the coils are smaller, they need to get hotter to perform the same, because there's less surface area (less coil-to-juice contact). Although the .2ohm build needs to get hotter to compete, it actually takes much less power to heat them (that's where it gets confusing lol

).
I'm only giving a long explanation because I was confused about the same thing a while back lol, and I wish someone would've explained it to me

.
So,
1.2ohm setup
needs 6.9volts
for 40watts (and only needs
6 amps to achieve that power)
(Same 40 watts, but .2 needs ALOT less because it's smaller.)
0.2ohm setup
needs 2.8volts
for 40watts (needs more at
14amps because there's less resistance.
The amps are higher on the low resistance because it's more "wide open". A good way to picture that, is to imagine the less resistance you have, the wider/more open a garden hose is, thus the faster the water comes out, thus the more amps needed. The 1.2ohm setup is resisting 6x more (the hose is tighter, more restraining on the water/amps), the .2ohm setup is getting close to not resisting at all, so it's a 6x wider hose letting the water/power through much much faster, so it needs quite a bit more amps.
Sorry hope this didn't look like a "lecture" lol, it's easy to remember that Watts = same heat on all coils, that IPV3 is made to heat bigger coils up as fast as you could normally only heat sub-ohm coils at, but keep in mind that takes alot more power. Smaller coils require less power for more heat, they're more efficient, but with less surface area. And your amps don't waste battery, you only have to make sure your within your battery's amp limit (which your IPV3 does for you I believe).
This is how I learned volts, amps, watts, and resistance:
Ohm's Law Calculator
I'm sure you've already known about this site, but after playing with it for a while it's super easy to catch on. I can pretty much do it in my head now

.
Hope this helps brother! Vape on!