I would think the vectoring guide should have some info about this, the BSR section?
I don't use this, so I'm guessing. But if the expected wait time is 100seconds, then an adjust by 10% will effectively make the wait time 110 seconds or a wait time that is 10% worse than it really is? This means, that you would not want to "consider" this location/skill as much as other location/skill with 0% adjust by?
sorry, no help with documentation.
-y