In what type of contract is the seller reimbursed for all allowable cost for performing the contract work and recieves a predetermined fee based upon achieving certain performance objectives:

A:  Cost plus fixed fee

B:  Cost plus incentive fee

The confusion from my part is that both are predetermined?  Or is the clear distinction the fact that the fee in a cost plus fixed fee is mandatory (Legally binding) and a cost plus incentive fee is based on discretion?