How does ARRI saturation formula differ from the ASC-CDL spec? In the context of ASC-CDL, saturation is applied as:

luma = 0.2126*iR + 0.7152*iG + 0.0722*iB
oR = luma + saturation*(iR-luma)
oG = luma + saturation*(iG-luma)
oB = luma + saturation*(iB-luma)


However, in the ARRI Look Files in the ALEXA Camera whitepaper they say:


  Note: The ALEXA saturation parameter differs from the ASC CDL
  saturation.


But they don't specify in what way, and I can't find that information anywhere.

Does anybody know?
I would imagine it has something to do with the white point/primary chromaticities are Alexa Wide Gamut vs. Rec709.

http://www.arri.com/camera/alexa/learn/log_c_and_rec_709_video