The instructions for my oven specifically say to lay bricks on their sides around the base in step one…phase two. However, I notice in the gallery that many ovens were built with bricks laid flat…a look I much prefer. Does it really make a difference?
Firebrick are typically 2.5" in height when laid flat in in the herringbone position.
Standard brick (edge brick) are typically 2.25" in height.
This would make your cooking surface brick (hearth) about .25" taller than the edge.
By turning your edge brick on their sides, they are now 3.5" in height. A full inch taller than the firebrick cooking surface - AND THIS IS GREAT as you can now add another 1" of insulation (or sand) under the firebrick cooking surface. The performance of your oven will increase w/ that additional inch.