Stupid question, but are you sure your fused claptons are 100% stainless steel? Sometimes the wraps are kanthal...that would surely mess up tc.
Err...it shouldn't? I've used SS/Kanthal Claptons in TC and it works fine. The outer wrap wire of a Clapton hardly affects the current path at all. To understand why, think in terms not of resistance but of conductivity, the inverse (reciprocal) of resistance (S = 1/Ω). The outer wrap is real thin and
suuuper long; as a consequence, it has a very very high resistance and, as such, a very very low conductivity. Let's do an example, using nice round numbers for simplicity:
Say you have a core wire that's .1 ohm, and an outer wrap that's ten ohms. The units of conductivity are sometimes colloquially referred to as "Mhos" (℧) but technically, they're called "Siemens" (S). The core wire, with .1Ω resistance, has a conductivity of 10 Siemens (1/.1) and the wrap wire at 10Ω has a conductivity of .1 S (1/10). Adding these together (yes, conductivity is cumulative in parallel) we see the whole wire has a total conductivity of 10.1 Siemens. Flip (invert) that one more time to get the ohms and see that we're at 1/10.1 = .099 which is very very close to the .100 of the naked core wire without a wrap.
Note: "very very close" is not exactly the same, but it
is very, very close. The resistance of a cold Clapton is very very close to the resistance of a cold naked core wire. The resistance of a
hot Clapton is also very very close to the resistance of a hot naked core wire. If TC is functional on the resistance changes of the naked wire, it should function on the resistance changes of the Clapton, also. You can get a (very very close) approximation just by using the preset for whatever your core is made of; if you want even more accuracy, you can get a custom TCR value from the Wire Wizard tool at steam-engine.org.