There's the package pay, stop pay, and there used to be what they called a 'core zone' pay based on time spent to deliver packages in each zip code. If it took 8 hours to deliver 40 packages in a zip code, you could get $135 a day or more. If you could deliver 120 stops in a zip code in a day, you might have a $0 core zone.
I was able to manipulate core zone pay a bit by not completing a zip code before going to the next zip code, and then doing a stop or two on my way back to the terminal. Plus another trick- instead of counting your time out of the terminal, fedex only counted from first to last delivery. So if you had a long route out 100 miles or more, your work hours looked longer if you delivered a few stops on your way back. Once I learned that, I was making an extra $25 a day.
So if you spent only 6 hours out of 9 in a $135 core zone, and 3 hours in a $60 core zone, you might take home $110. But if you made the computer program 'think' you were in the $135 core zone longer by spreading out your deliveries, with the same number of stops, you might get $124 a day. The $135 zip code I had went from $98 to the $135 after I figured out the system. Also had a $89 core zone get up to $105, and some with bigger increases but with less stops in a high core zone, it didn't make much difference. I was delivering in 6 or more rural zip codes daily, with up to 400 miles, Some days I could manage 80 stops, then other days, getting more than 30-40 was a full day.
Plus you got a fuel supplement based on average mpg, not your actual usage. So if you had an efficient vehicle or good driving habits, or lots of highway miles, your cost of fuel was actually reduced to less than the cash cost.
The attorneys in the lawsuits still don't quite understand the complexities. I don't know if they are still using the core zone system with ISP model or if it all rolled into base pay.