These vessels are going to go into shore from some distance out.Wow quite a beast
Just curious, I did not notice any rear facing weapons, any reason why?
Like maybe another 30mm/CIWS in the back to defend against missiles from from the rear?
The big fans would block the line of sight for the front mounted 30mm's if a missile was skimming close to the water
Or would a support ship help screen the rear?
They may address a relatively small issue where the opposition has little or no sea or air power. Or they may be a part of a larger task force that will have had to contend with and defeat opposition air and sea power before these vessels are sent in.
In the fist case, they will not need such weaponry.
In the second case, if they do need such weaponry against either air power or sea power that is able to break through to the amphibious assault group, then the entire operation will have been put at severe risk.
Anyway, as you state, and can see, having AK-630s or other weaponry oriented to fire aft (short of VLS weapons that can rise above the large fans), those three large fans which provide the craft its thrust, are simply in the way.