ideal oven stone size and bread placement

My oven stone is darn near as big as my whole baking rack in the oven.  I worry about enough heat getting around it to balance the heat in the oven properly.  Does anyone have any sort of magic formula or scientific calculation regarding this?  The ideal ratio of baking stone area to oven shelf area.

Also can anyone talk a little about the pros and cons of placing bread higher or lower in the (non convection) oven?

thanks for any help.

Pablo