Hello, I think Dave will want you to have the openings adjust independently. That way you can control the fire with the lower vent and the airflow with the upper. The airflow is necessary to allow a more even heat. A lot of time I have the lower shut down with just the upper open. I use propane to start, Lump Charcoal and wood.. I just hope your vent exhaust is large enough. As I said I had to modify mine from a 3" exhaust to a 21/2 X 17. It allowed the FB vents to provide the flow necessary to even temps. It takes mine awhile to settle and I have the Cookbox insulated well plus the flue is encased in an insulated Chase. Keep in mind that mine is a wood frame cookbox with only the FB in metal and block. When I am running well I can keep top and bottom within 5-10 deghrees.
Look for Dave's reply = He is a GURU re the RF for sure. Good luck. I just finished a bunch of pepperoni and sausage