Using my corporate booking tool, if I try to buy the following flights, it prices out at only $426.21 due to an M-up fare on the SFO-JFK leg. But, I only see this when I force it to book me a First class seat on those flights. The search results page indicates the fare is ~$1,100.

So, my question is, how do M-up fares work at Delta? Using Delta.com, I only see discounted A-class fares in first, but nothing about Y/B/M fares with an auto/instant upgrade. I'd like an easy way to find these types of fares... not sure if it's unique to my company or part of a broader program?

10/25 - DL 724 SFO-JFK FARE BASIS-MA00UPRR/CCHZ
10/26 - DL 6764 JFK-CLT (in coach, as it's a CRJ)