Going back to the 'stacking' thing, I tend to go by the 'different systems, similar effect' theory. You can run Thermo and Low-Light at the same time; they don't stack, though they do overlap
Thermographic moves your vision penalties up one column, right? Okay, good. Low-light moves Dim or Partial up to Full. That's fine too. But Low Light is not going to move thermographic's "Total Darkness to Dim" up to Full; that's stacking. Overlap means that you take the better, and only the better - Dim to Full with Low LIght (instead of Dim to Partial with Thermographic), and Total Darkness to Dim with Thermo, because Low-Light doesn't work with Total Darkness.
Take the best, not take one, then take the other.
