Perfect bottom, not enough on top
I've started putting my 2 cordierite kiln shelf pizza stones right on the burners of my Weber Genesis gas grills. On high, the stones can reach over 700 degrees, which incinerates the bottom of the pizza in under a minute. Putting the burners on medium-low keeps the stones between 550 and 580. I place the pizza on one stone, and then place the other stone about 4 inches above it (resting on the ledge where the grill grates would have gone), essentially sandwiching the pizza between the two stones. But while the cheese melts, the crust on top is not browned at all when the bottom is perfectly leopard-spotted and crisp. I've been finishing them under the broiler of my oven for about 60-90 seconds. What do I need to do to synchronize the cooking of the top and bottom? I really don't want to lower the heat of the stones - the pizzas cook in about 4 minutes with great oven spring and I don't want to lose that. Thanks.