Something
is way off - the technology and its ability to reliably and repeatably gauge temperature with current equipment/setups.
500 is not 500 when it comes to TC - one device+build combo might be super hot at 400, another anaemic before 500. In reality that '400' will actually be getting much hotter and the '500' is cooler. Busardo demonstrates that in his Yihi SX Mini M review where he talks about setting his Squape and Kayfun4 at about 280, and then measuring them with his fancy FLIR temperature sensing camera to be well over 400°.
In his case he had a bad setup on the KF4 (apparently the stock KF4 requires you not to use the juice control ring with TC as it changes the tension on a spring which messes up resistance) but it does serve to demonstrate the myriad problems possible across the range of vaping hardware and builds we have/do.
There's a lot of factors, one of which is the inherent resistance of the atty and its connection to the mod and to the coil. That can often be as high as 0.03 which, with Ni200, can be equivalent to a temperature of 90°F. A Kayfun4 is again an example of an atty that has been measured to have a high static resistance - 0.03 was measured by a guy in my thread discussing vaping on non-Ni200 TC wires (
link to his post.) That whole thread may be of interest if you've not seen it as it touches on a lot of these points in various places.
This is (yet another) reason to use Titanium whose starting resistance is much higher, such that static resistance in the surrounding devices cause less inaccuracy. Though the reduced Temperature Coefficient of Resistance of Titanium also means that there is less resistance rise to measure which counter balances some of that advantage, but not all - the coefficient is half that of Ni200 but the starting resistance can be up to four times higher.
Another possible alternative is the new Resistherm wire being popularised by Dicodes which has a similar coefficient to Titanium but is meant to be even easier to work with.
Anyway, yeah it's all very imperfect at this time
And Ni200 coil heads are notorious as being among the worst for inaccurate temp sensing and thus needing strange temperature settings.