Some of the best lines I have ever gotten have been while being near the bottom of the line holder list.

I have been told it has to do with coverage days/trip availability. When you are near the bottom, pretty much every day of the month is a coverage day, and since you can't work everyday and there are only so many trips available once the computer gets that far down the list (limiting its ability to build 90+ hour lines), you end up with better schedules.