TC1 works out to around 500ppm/degC for high_po and -1500ppm/degC for xhigh_po. Anyone know if this is accurate/suspicious?

The xhigh_po is new in this process, so everything about it should be taken with a bit of skepticism. The high_po is established from previous versions of the process and should probably be good, but I'll see if I can find anything documented about the temperature coefficient (from experience, I'm not expecting to find much, but you never know).