Lavatory Faucets - gpm

We are having a little trouble with the flow fixture table calculations. We specified Sloan automatic sensing faucets. According to the Additional Guidance document 8/16/10 we're supposed to list this as a "metering faucet" type and calculate the gpc per the manufacturer's data. I assumed that the fixture would adjust to a 20 second run time, which is the Centers for Disease Control recommended handwash time and calculates out to 0.17gpc. Compared to the 0.25gpc typical from LEED guide table 4 we would get savings. However, the plumbing engineer and I have checked with Sloan and they say their controls for the autosensing faucet only go down to 1 minute, not 20 seconds, so the faucet will shut off a) after the user removes their hands or b) after 1 minute. So do we use user behavior patterns (average person keeps their hands under the faucet for 12 seconds, gpc = 0.5*12sec/60sec = 0.1gpc? I am curious how you arrived at the 0.17gpc value for the Toto fixture? I see on toto's faucet info they use 10 sec cycles. If the hands are still under after 10 sec does it begin another cycle?