It's because for the 7M, Toyota numbered the coils based on the cylinder they fire (1 and 6 is C1, 2 and 5 is C2, 3 and 4 is C3), so the firing order is c1, c2, c3, c1, c2, c3 etc.
For the 2JZ-GE DH-61 equipped cars, the coils are numbered from front to back in the valley between valve...