Rotoflex steaming question

I've been baking out of a Rotoflex deck oven the last few months: it is a 4 tiered deck oven with steel decks.  The top gets too hot and the bottom doesn't get good top heat, so I've been cooking on the middle two levels.  I had been using a garden sprayer to steam the loaves, and got acceptable results.  However, I had to leave the door open a lot and be pretty active during the cooking period.  I recently rigged a mister inside the oven.

Here's my question: the level of steam is great, but the bottoms of the lower level loaves are burning pretty bad.  I have it set at 450, but the lower decks are heating up pretty hot.  My thought for a solution is to preheat it to 400 and then cook at 450, but that would really only be good for the first load.  Any other suggestions?