Using a fresh config file & the latest version of TFC, I restarted MC after changing cyclicTemperatureRegions from true to false, made a new world, and it doesn't quite work.
From 0 to -20k Z (North), it works as expected.
From -20k to -40k or -45k, it cycles back to warming up to the temperatures you'd expect around 0 Z, despite that setting being set to non-cyclical ("If you want an endless north / south with a temperate equator, set this to false.").
Beyond that, no matter how far north you go, the temperature is pretty temperate, with the minimum temp ranging from about -4 to 0 C.

• TFC Version: 0.28.1.111

I'm assuming this is the same problem as #637, in that we internally calculate the period of the sin wave (and thus the cutoff point for non cyclic temperature regions) to be twice what it should be

This bug exists in the current version of TFC, which is -MC1.12.2-1.6.1.157.
For more context, the current version of TFC doesn't use "cyclicTemperatureRegions=false" anymore, but "S:temperatureMode=", which is set to "ENDLESS" in this case. I'm using the following settings:

    # If Cyclic, this controls the length (in blocks) of the temperature regions. The temperature values change in a wave-like pattern (sine wave).
    # Wandering straight in a direction increases or decreases temperature. When you travel this many blocks, the temperature begins changing in the other direction.
    # Min: 1000
    # Max: 1000000
    I:latitudeTemperatureModifier=1000000

    # This controls how temperature is affected by how far from equator you are.
    # Valid values:
    # CYCLIC
    # ENDLESS
    S:temperatureMode=ENDLESS