Again, it depends. Look on the EOB. Is there anything about U&C or R&C? If so that means it's based on the standard calculation (HIAA 90th%) You can appeal, yes, SOMETIMES they will release more.. nearly never will they release all. In cases with R&C/U&C appeal the insured stands a better chance at appeal, ultimately the responsibility is theirs because again, it's Out of Network. When dealing with R&C/U&C there really isn't an "allowable" like with participating.
Just a side note, but this is EXACTLY why physicians should NOT bill "allowable" fees per network. The rates carriers use is based on a standard calculation BY geographical location, this is a problem when physicians try to cut back on their adjustments (which makes no sense to me) by billing the allowable per plan, that means the charge being captured is going to be LOWER. So not only does it mess up reporting features when you want to capture data based on adjustments but your also giving the insurance carriers lower fees which will result in lower reimbursements.