Every firing is different! In this case, the amount of flat ware lead to tight vertical stacking of the shelves which caused temperature zones in the kiln, preventing the stack from drawing early in the firing. This happens because the shelves baffle the movement of heat throughout the kiln, especially down to the flue. Heat naturally rises and collects at the crown of the kiln. We had red heat at the top while the flue was dark. We also had back pressure at the ports, indicating a reducing atmosphere. This is a potentially serious problem early in the firing which can lead to "black (or carbon) core" in the clay walls. A piece reduced too soon will be "punky" and fragile. It will lack that familiar "ring" when tapped. A pot with a dull thud and no obvious cracks may mean the walls have black coring.
The solution was to induce draft by starting a small fire in the stack. Just lighting a piece of paper and dropping it through the damper plate slot does the job. You can immediately feel the pull of the stack by placing your hand at the damper opening. You now have draw and heat will be pulled to the bottom of the kiln. In the interest of safety, you can place a lighted match or candle at the opening. You will see the air being drawn in.
An opening in the stack is known as a "check draft." The stack pulls in cooler, outside air through the check draft. But you should be very careful when putting your hand near the stack. More importantly, putting your hand (or face!) close to any chamber port is never a good idea no matter what the temperature of the kiln. For ports, the "stick test," placing a stick into a spy port and watching to see if the resulting flame at the tip is drawn in or is pushed out, is best to determine draw or atmosphere. It's a handy tool since it works in some situations that don't provide normal visual cues, like the bottom spy port.
Down through the years I have seen kiln plans with "mouse holes" at the base of the stack. They are there for inducing draft just as we did. But if the stack is tall enough, an opening at the base should not be needed (fun to include in designs for teaching purposes, though). And placing the damper in the stack provides an incidental advantage, as we found out.
Yes, you learn a lot with each firing. And yes, it is complicated at first. With experience you will learn to read the kiln. The senses will tell you everything! I like to hear comments like "there isn't as much vapor from the stack this firing," or "this firing seems faster." Being aware and paying attention to detail is important. Keep your head "in" the kiln and your senses alert to what is going on around it. And take good notes (I should talk!).
Good craic as the Irish say. I am anxious to see the results.
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