Why an all-forward main battery can limit a battleship

What was wrong with an all-forward main battery for the King George V class?

The arrangement is judged unbalanced, and even Nelson's all-forward turrets could not all fire directly ahead.

Moving the King George V class's main armament forward is rejected as an unbalanced arrangement. Nelson and Rodney show that an all-forward battery does not mean every gun can fire directly ahead: one mounting obstructs another. Bringing all the turrets to bear ahead would require a progressively higher arrangement. The prospect of stacking quadruple turrets this way strengthens the preference for distributing the battery.