Don't overthink this, it's really simple. Instead of looking at holes in the top, you'll be counting revolutions. Most of the time, you'll be less than one anyway to maintain temps, I'm usually 1/4 or less for lo/slo's. I haven't played with the dual lower vent, I'm always using the cyberq. The only time I open things up a lot is for steaks, and even then, once I see 700°, I go down to about 1 open to maintain.
Robert