LP, you have some very good points there. I think we are following a similar philosophy. Let me try to rephrase to see if you agree. The key is obviously to have the stone-to-air temperature ratio to be just right so the top-to-bottom cooking is even (plus all very hot of course!). This is difficult to achieve because the stone has a tendency to keep heating more and more since it is closer to the fire, and to get ahead of the air temp. But there is a point during the heat-up when the stone and air about match, because the stone takes a long time to heat up and so at some point the stone temp just catches up with the air. If you throw the pie on at that equilibrium point, and maintain it through each successive pie (perhaps by lowering the burners a bit at points to cool the stone down), you have perfect pizzas. On top of this, anything that can be done to insulate the stone and to provide radiant heat from above also helps by balancing out the temps (aluminum under stone, raising stone, bricks above pizza to radiate heat down). This will increase the size of this "sweet spot", making it easier to hit consistently.
Right now I am using a huge brick right above the pizza and am raising the stone off the grill with bricks. It was taking too long for the stone to heat up with foil so I stopped using it for now. I have found the temperature doesn't dip for too long when the grill is opened, as long as I only open it just enough to slide the pizza in -- my thermoprobe shows the temperature recovers in 30 seconds. The pizzas are coming out pretty good but are not yet consistently good; I am hitting about 2 minutes cooking time per pizza.
Jason, your idea sounds a lot more sure-fire, but less authentic. If it makes a great pizza, thats what counts.