First I would recommend that you work with a Realtor that can give you specific information as it regards to this particular property and your local market.
But, essentially what the bank is going to do (with your offer or any other offers) is to get a 3rd party "price opinion or appraisal" to make sure that whatever offers they are considering, the property is being sold at a comparable market price.
In effect, they are going to want to make sure that the bank is losing as little as possible.
I have seen short sales sell at $10,000 below asking price, and I have seen them sell at or above asking price.
There is no "standard percentage".
Hope this helps. Good Luck