See screenshot:
http://imgur.com/BoTKVxI
The area inside the walls is not big enough for those turrets. They cannot fit, it's impossible to build this yourself, the walls and turrets overlap. I think it's a leftover from when turrets were smaller in an older version.
[12.26] Impossible turret configuration in new hope level 4
Re: [12.26] Impossible turret configuration in new hope level 4
Thanks for the notice, fixed for 0.12.27.