Yeah, that's my experience too. If you're doing strictly follow depth chart, and you list a starter and backup for each position, you'll get in the range of 34-37 minutes for the starter, with the rest for the backup, when you loose (or the score is close).
If it's a blowout win, then it depends on when the garbage time kicks in. Typically I see 28 min starter/20 min backup, but I've also seen 25/23 split