I am only using one flash. I thought he incident meter (with the dome on the 558) was giving you a setting to correctly expose a 18% gray card. I will try metering a gray card and see how the results differ. My thought is in auto mode the flash cuts out the light when it determines enough light has reached the subject to properly expose an 18% gray card. Doesnt the meter do the same thing? Maybe I just burn a roll through the 645 to see real results.