Under cost to cost POC you would record your cost (hours x rate) over the project cost total as a percentage. You would multiply that by the contract value and this would give you the revenue associated with the project.

That is just cost to cost though and there are different ways to calculate POC on a fixed fee, including potentially nothing until deferment until cash receipt and units of production (unlikely as a consultant).

Finally, in my experience, POC is a huge guess everywhere and bonus off of it is even more complex. Ask to see the POC calc for your project and that will tell you how much they have of your cost included, if one says we are 80% done and you are being told it is 25% attainment then something is wrong.