idk if updates ever changed it, but back when I first started playing (day 1) building walls around the max settlement area didn't really work.
Enemies could spawn inside the walls
So what I'd do is wall a very small area, then have ladders etc going up to higher levels for my workbenches, storage containers and important stuff including generators.
Concentrate on more firepower instead of walls. Give miniguns to your settlers...if you have the DLC you can build sentry bots![]()