thanks for all the help everyone! we went ahead and tried before we had all your help, but what we did was heat only one side of the grill to full temperature, and then cook the pies over the unheated half. A thermocouple measurement of air temp near grill surface gave 600 degrees....
Ok, no tiiles and using indirect heat is an interesting approach. I'll have to try indirect heat
to see if I can obtain my target temperatures. Yeah, I'd say that adding tiles will give you
more control over temperature. The trick seems to be in monitoring and selecting the tile
temperature at the moment you put the pizza in.
If you desire a crispier top, then try starting at a lower tile temperature and crank up the
heat to full. For example, crank up the heat to max while monitoring the tile temperature.
When the tiles hit 500 deg F., place the pizza on the tiles and close the lid. If you want
crispier tops, then load the pizza when the tiles hit 400 deg F.
Another idea is to add some kind of metal heat shield to the lid that would keep the heat
down lower to the top level of the pizza. This way, when you cranked up the heat there
would be much less volume of air to heat and the air at top level of the pizza would come
up to temperature much quicker. Makes sense?