Spoke to a supervisor at AAdvantage Customer Service.
This is what she said:
500-Mile EQM Minimum applies BEFORE the bonus for class/booking code.
FNT-ORD booked in Y (Full-Fare, 223 Miles) would earn 750 EQM (That's the 500-mile minimum plus the 50% bonus for booking in code Y). The same flight would earn 1000 RDM for a PLT (500 minimum RDM + 100% bonus) just as before. That is, until the change in the second half of next year to how RDM is calculated.
Hope that helps people who are trying to set up their spreadsheets like I am.