I got 6,500 troops total, its 1,625 per fort. Also the navy isn't anchored in the open at Lake Guard, its located in the small lake east of it. Basically, you have to break down the entire fort to get to the navy. I think it should be reasonable that Lake Guard is built mostly of stone, I mean my nation wouldn't build a fort that could easily be destroyed by a navy. The fort has to defend against naval attacks. if it isnt reasonable in your view then dont have it affect anything.