While I'd agree that pre-built Ni200 coils could never compare to a DIY 70W Kanthal coil I'd even go one step further and say that that for the most part 'high power' in TC does not really exist as most TC mods on the market top out at ~50W in TC mode.
I am however wondering where you got the temperature values that I highlighted and underlined above. This is ether testament on how horrible TC mods 'guess' the actual temperature of the coil or is just one users observation/opinion and not really based on anything scientific. (or a little of both)
Considering that I've checked the TC mods that I use with the 'dry cotton test' and I regularly use %100VG at 380F or lower, I'd say that the "550F" value for VG is rather suspect as well as the PG value. (last night I was clouding up my living room with a single 10 wrap 2.5mm 28AWG coil built on a TSV4 single coil deck @ 340F with 30W and DIY %100VG juice)
Juice blends with PG content will produce more vapor at lower temperatures than strictly %100VG juices, however the values you posted appear to be invalid based on my own personal experiences.
The OP has a Sigelei 150TC, which can output
100 joules in temp control mode. That's certainly enough for "high power" TC.
Not trying to sound like a dick, but those values you underlined are, well, chemistry and well proven. Sure, from your observations, you're definitely getting vapor at
displayed temps far lower than the boiling point of your liquid, but keep in mind that heating is
never uniform.
Go put a pot of water on the stove, turn up the heat, and watch it for a little while. You'll get a bit o' steam out of that pot
long before it's fully boiling, but if you stuck a thermometer in there, it would still read below water's 100c/212f boiling point.
But obviously, some of that water IS boiling, thanks to non-uniform heating. Eventually, the whole mass of water exposed to the heat will catch up and it'll be at full boil and show 100c throughout the volume. But it won't ever EXCEED 100c either, until the water is all gone.
Throw pure VG in that pot instead of water, same thing will apply, you'll start to get vapor long before the whole mass registers as ~550f, and once it hits equilibrium, it won't exceed that temp either, until all the VG has turned to vapor.
Same thing with the surface of a coil, it can't exceed the vapor point of the liquid until there's no longer any liquid in contact with it. That's why I told the OP he was probably used to vaping around 520-550f with his 70w Kanthal builds ( exact temps depending on how the mix of his juice impacted the vapor point).
Now, to get more specifically to temp control and coil physics, watch how a coil heats, even a
spaced coil heats from the inside out (even though it seems uniform to the naked eye, it's not), so it's always hotter sooner in the middle than on the ends (unless there's a build problem, hot leg, etc, but that's a subject for another time).
The thing is, temp control as it exists right now can't tell that the middle is hotter than the outside or legs, all it can "see" is the average resistance of the
entire length of wire (and that's why the long legs on prebuilts suck, since they tend to amplify the problem).
Anyway...while the middle may actually be 550 (or higher), the outsides and legs won't be, and as a consequence, the resistance seen will reflect a lower than actual peak temperature on the display until (if) the rest of the coil catches up, but it's still getting warm enough
somewhere on that coil to vaporize
some of the liquid in contact with it.
On top of that, vagaries in wicking can create spots in the coil that are hotter(too little wick, clogged/choked section of wick, gravity as you tilt your atomizer etc).
