What a mess! After speaking to my accountant and an accountant involved in this situation (both are senior partners for one of the big four firms) this seems to be a very complicated situation. From my understanding:
1. The guidelines are very poorly written and leave too much to interpretation.
2. Accountants on both sides can not agree on the accounting procedures with regards to the guidelines.
3. The categories involved have nothing to do with the car's performance.
If it were to involve Newey's compensation I can understand the potential difficulty. In my case I received compensation from HRD in my name where benefits and certain taxes were paid by the latter. I also submitted invoices to HRD from my one person corporation and received compensation where payments were made in the name of both myself and my company. In HRD's eyes, I was considered a 100% employee.
Another scenario I have seen on several occasions over the years was the following:
Team A's principal earns XX million US dollars a year and team B's principal earns YY million dollars a year. YY is 12 to 15 million greater than XX. Team B's chief engineer in a given department is paid substantially less than team A's per year on paper. Team B's principal says to his engineer, I realize the difference in pay from your counterparts so here is a "Christmas gift" from me as a thank you which makes up the difference. There is no official record of this. So IMO, this budget cap policy is a farce and has too many paths around it.