Seniority is a driving factor. So is the FedEx deadhead policy. If you live near a major airline hub (ORD, DEN, DFW, IAH) you can focus on bidding deadhead trips and using your bank money to get to and from work. If you can't bid deadheads, you are stuck competing with a bunch of guys all trying to jumpseat to Memphis on a decreasing number of jumpseats.
If you live in a smaller city served by FedEx (BOI, BIL, ICT) you will have less competition for FDX jumpseats, but also take the risk FedEx will decide at some point to stop operating out of your city.
I live in a location that is a hybrid of both. Near a major airline hub and a smaller FedEx facility. That gives me deadhead and jumpseat options. Being in the middle of the country near a large airline hub usually allows me to fit inside FedEx trip bank limits 95% of the time.