The FedEx Carrier.php is using 'LIST' as the value for 'rateRequestType' which is consistent with FedEx documentation on their developer portal. However, according to FedEx support team the documentation is incorrect and the value should be 'ACCOUNT' otherwise retail prices are returned instead of the account-specific (highly discounted) rates. The discrepancy can be considerable and highly affecting the operation.
If replacing 'LIST' with 'ACCOUNT' is not an option, exposing this parameter on the configuration page would be great.