Look at the recommended size for intakes and use that to size however many you actually want. If it said 90 sq.in. and you wanted 3 intakes, make them 30 each.
For a RF cooker the BP runs from the top of the FB across the CC to force the heat/smoke to flow over the food and out the stack at the FB end. Tuning plates are used in a traditional offset with a stack at the opposite end of the FB.
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