Stainless steel dome pizza ovens heat up much more quickly than cast refractory ovens, and they rely on the heat of a live fire for baking pizza and other dishes to a greater extent. Because of this, it is important that your fire has the ability to bounce off the oven dome directly onto the oven floor and your food.
By designing our pizza ovens as rectangle, we make it easy for this to happen. Your pizza oven has space for a live fire on one side of the oven, and a fully heated rectangle on the other side. The heat from the fire bounces directly off the dome onto the cooking floor for even baking and no cold spots.
On the other hand, if a stainless steel pizza oven is square, or even deeper than it is wide, then there would be significant cold spots, either in the front or the rear of the oven, as well as spots that are inaccessible for cooking in the back of the oven.