Why can a ship need thicker rear belt armor?

Why is the rear belt a whole inch thicker than the forward belt?

The extra aft armor is being used to balance the modeled distribution of turret, superstructure, and machinery weight, although real ships would also rely on structural and deck arrangements.

The unequal belt values correct fore-and-aft weight distribution around the forward turret, superstructure, and machinery spaces. In the model, adding armor aft conveniently offsets the concentration of weight forward. This is a game solution rather than a faithful rule of naval architecture. A real ship's deck structure and internal arrangements would also contribute to longitudinal strength and stability, so the displayed belt values should not be treated as universal.