Barbette Armor of the Battleship Mutsu

I noticed something odd about the armor near the first turret of the battleship Mutsu, so I submitted a bug report.
However, it seems that Hiraga Yuzuru’s drawings alone are not conclusive, and I am at a loss.
If anyone has any blueprints of the crucial parts, I’d appreciate some help.

For more details on the issue, see this report.