580EX wireless ratios - incident or relected H:S?

I've read the 580EX manual and tutorials I can find on line about setting ratios wirelessly with a pair of 580EXs or 580EX / 420 EX combo, but none explain if the ratio numbers actually represent relative incident strength or reflected H:S ratio desired in the photo.

The fact they include a 1:1 ratio would seem to indicate they are incident power ratios, but the power output is actually based on measurements of light reflected from the subject from each unit, sequentially. How much light is detected by the camera will depend entirely on how the light is striking the subject as viewed by the camera.

For example, consider a standard short lit oblique pose. Fill is placed over camera, with key light an equal distance (not required but for benchmark purposes) 45 degrees off the subject's nose, or 90 degrees from the camera axis. When viewed from the camera the fill will appear to illuminate the entire subject, but the key light only parts of it (the highlights).

If studio strobes or manual flashes were used at equal power and distance their 1:1 incident ratio and the overlapping of fill and key lights would produce a 2:1 highlight / shadow brightness differential (i.e. reflected lighting ratio).

I understand the individual firing / evaluation sequence for Canon wireless(See "How Wireless e-TTL Works at http://photonotes.org/articles/eos-flash/index3.html ) but what isn't clear to me is how the camera can determine the relative power output level needed by each light based on reflected readings from each flash fired separately in sequence when the fill light illuminates the entire front of the subject but the off-camera light only strikes a much smaller area as in the short-lit / oblique pose described above. My guess would be that the camera only uses the brightest area detected for each flash zone (i.e., A:B) rather than an average of the entire scene.

How do you set a dual 580EX ratio to achieve the same 2:1 ratio of H:S brightness you'd get with manual lights positioned as described above (equal power / equal distance): 1:1 or 2:1? How would you set the ratio if a 3:1 reflected H:S ratio was desired?

If someone has a pair of 580EXs I'd be interested in seeing a short-lit oblque pose shot at 1:1, 1:2, 1:3 etc. ratios. There was a test linked in another thread, but it was cross-shadow lit (lights on opposite sides) which doesn't address the issue of overlap of the lights with respect to the ratios.

CG