sonoran

I purchased an Ameristep harness last season but never climbed into my stand - just still hunted all season. I will, however use the stand this year.
I cannot find the instructions for this harness. It is model 227. I know how to put it on but cannot figure out what one of the straps are for.
On the back there is the brown webbing that hooks to the strap around the tree. But there is another strap just below this, a small strap, that is the same camo pattern as the harness and is attached to the middle section of the harness.
Can anyone tell me what this is for?

Thanks,
Sonoran