Houston,
Who said that pro driver is only 4.5% castor?
Found the following on the Byron website:
Synthetic/Castor Ratio: The ratio of synthetic to castor is engineered specifically for the application. Performance Blended Premium Sport Fuels are blended with an 80:20 ratio of synthetic to castor. RACE Gen2 fuels (Except RTR20 Gen2 and RTR33 Gen2) are blended with a 50:50 ratio of synthetic to castor.
So it would seem that 9% total oil would be 4.5 % castor and 4.5% synthetic.