In this image I have left the red lines off the cell divisions. If you click the picture, and blow it up, you can see the faint divisions of the cell dividers imprinted into the plastic cover.
When you look close at the cell layout of an 8D battery you can clearly see that these cells are SQUARE! The 4D has rectangular cells, which can be better situated, the 8D has no optimal configuration.
Because of the square cells on an 8D battery there is no orientation that is better than another. Any way you install a flooded 8D battery, on a monohull sailboat, will result in the plates uncovering when heeled. This is never good for the batteries.
I do not and can not recommend 8D flooded batteries for use on sailboats.. Use at your own risk and if short life is an issue you'll know part of the reason.