It says you should cover up to 40 percent of the front of the oven to retain heat.
However, it looks like they tell you to just use whatever veneer you chose to do so.
I don’t understand why you would use all this fire brick and high temp mortar, just to slap a common veneer on the front with no protection from hear behind it. Thoughts?
Yes. The “outside” of your oven is the area outside the heat envelope. The raw opening is the inside of your oven. Until you have brick of some kind to form a heat shield, that area can’t take veneer on its own.