EOB's are excellent sources of data on allowed amounts. I keep a cheat sheet of my most common codes with the allowed amounts by carrier. This helps me to have some idea what will be allowed so I know what to collect upfront. This will not be exact, as reimbursement will differ, but this will get you fairly close.
Review all EOBs as soon as they come in. More and more plans are moving toward 60 days from date of EOB to dispute a claim. Do not lose the ability to get correct payment.