Marie, air is an insulator. It's what saves people hundreds of dollars in fuel costs when utilized in double paned windows. In order to prevent the intense heat from below going straight up into the stone and burning your undercrust, you need air between the deflector and the stone.
That's assuming, of course, you're attempting to use the pan as a deflector. If you're just using it as a way of getting the stone closer to the ceiling, then it's kind of doing it's job, and you might be able to get better results with a lower pre-heat temp for the stone (perhaps 575-600), but, even then, with the shininess of the aluminum, you could easily see widely varying temps on the stone (considerably hotter on the edges).
Grill setups rely entirely on lower ceilings and, to a lesser extent, deflection. Raising the stone isn't really viable for a lower ceiling, imo. If you want a lower ceiling, you have to add one. And if you want deflection, the deflector must be larger than the stone (a considerably bigger pan) and there has to be air between the stone and deflector. The gap can be as little as 1/16", but it still has to be there.
