Bread rising too much in the middle when using baking steel

Hi! 

I'm wanting to bake my bread on my baking steel because the bottom part of the crust comes out less dark than it does when I bake it in the DO. However, the two loaves I've done have really domed in the middle. The loaf baked on the baking steel is in the back, and the loaf I baked in the DO is in the front. I have a pan with lava rocks in the oven with the baking steel, and I added some ice cubes nearby in a tray as well to try to keep as much steam in the oven as possible. Any idea why the middle is rising so high like that? I make a 1,000g dough and divide it in half. Ideally I'd like to bake them at the same time, which is another reason I'd like to perfect baking on the baking steel.

Thanks for your help in advance!