I concur with your strategy, I was gave a personal anecdote to back it up.

I don't know about that map but here the raider attacks come from different side of the map. But its the same concept I think.

In the vanilla game, I had an idea to build small forts that had multiple layers as to concentrate the most amount of missiles and not get a huge workload I simply observed what directions the small bands of Raiders were coming from and then built a fort To block that path.

Just make sure you manually move children from building from the side the raiders attack to the other side of town.

Yea! Everytime I tried to build walls around the settlement I got super high workload. So instead I build a citadel in the center and hid when the raiders attacked. When they spread out and attack my buildings I opened the gates and charged out.

Interesting defence strategy. Haven't thought of that.