I thought since the fortresses are placed in a way which doesn't make a lot of sense. What if I built those coastal artilleries in Georgia and placed them where they can be really used effectively?
Coastal artillery are an expensive waste of limited resources. Units inside a fort don't resist an invading force directly. So the Union can land an amphibious force on a fortress and unless the stack is in assault mode, no battle takes place. The artillery will fire at passing ships, but the invader can starve them out or build up cohesion and assault on their terms. I was able to sea lift 12 Divisions into VA as the Union. The CSA cannot prevent this. Have a reserve that you can rail in, but don't spread your forces thin trying to hold the coast