Don't try this at home.
Masonry ovens cook differently than a normal home gas or electric oven. The latter bakes primarily by heating the air in an enclosed space, which in turn heats the food. A masonry oven relies more on radiation from the hot masonry to cook the food. Well, I knew this I guess, but the following experiment has proven how much different masonry ovens are.
Last weekend, I was baking my usual batch of bread - 5 loaves - which pretty much takes up the whole floor of my small-ish oven. My Lovely Assistant, on the other hand, had "brick oven roasted herbed chicken with new red potatoes and veggies" on her mind. Since I was particularly hungry and didn't want to delay dinner by waiting until the bread was done before putting in the chicken (which is how I usually work it), I slid the grill into the oven (the "grill" is a cast iron grill that has legs and is normally used to grill food over coals in the oven, though in this case, there were no coals in the oven), put the pan with the chicken on the grill, and loaded 2 of the 5 loaves of bread under it for simultaneous baking. Kinda like two shelves in a conventional kitchen oven, with the bread on a baking stone on the lower shelf, and the chicken in a pan on the upper shelf. At loading, the oven walls were around 600°, which means the oven air temp was around 500°, give or take a few degrees.
The three loaves that were not under the grill baked just as expected, done to a lovely, crisp, golden brown in 20 minutes. The loaves under the grill however . . . didn't. When the first loaves were perfectly done, the two under the grill were just getting started -- still pale dough. I had to move them over to the spot recently vacated by the now-done loaves to finish off for another 10 minutes or so. Although I had suspected that the loaves under the chicken pan would cook a bit slower, I was surprised by how much difference it made. Had I not moved them over, they probably would have taken almost twice as long to bake. In short, "shelves" don't work so well in masonry ovens.
This also helps explain why things baked in a masonry oven taste different (better, IMHO) -- the food is, in a sense, partially broiled by the hot masonry ceiling and walls of the oven as it is simultaneously baked. This makes for, e.g., a wonderful, crispy, crusty skin on chicken, which was, BTW, delicious, as was the bread. ;-)