Considering that is only showing the main belt and deck armour, it’s not listed there. You can, again, see it in the tabulation of the tonnage data right here, under “battery”:
I will also note again- the gun shields are LITERALLY modeled ingame. The lower gun battery has some armour protection, but for some reason the gun shield armour is not modeled, even though it very much exists, as you can see it. With your eyeballs. Like, it is literally right there. I can also post a photo of an actual casemate gun with its gun shield taken off the Mutsu where you can clearly see the gun shield is not, in fact, made out of paper.
