The hole in the costs regime for claims no longer continuing under the road traffic accident pre-action protocol

Where a defendant makes an admission of liability but alleges contributory negligence (apart from a failure to wear a seat belt) a claim will no longer continue under the Protocol. If the parties settle before proceedings are issued, what are the fixed costs payable by the defendant? It will likely turn on the meaning of the phrase ‘agreed damages’. Does it mean the sum before or after a deduction for contributory negligence is made?