Just checked, last time I did an upgrade from economy (E) to Domestic First was ORD-SAT-ORD and 1.100 points for each leg which kind of matches a 100% earning for the 1041miles as per great circle mapper. Actually, the UA upgrade messed up the SK ticket and both legs ORD-SAT and SAT-ORD disappeared from my SK ticket and were reissued on a UA ticket with P. Had quite a lot of phone calls to make to make sure, it won't be a problem....

So, I guess for the OP, they also reissued in P which gives 100% with a minimum of 600 points. And there we are. Mystery solved.