For mine, I just kept it to something simple. I went to a mall yesterday and had to park and the pillars and some of the items we already put down in the course reminded me of the dividers and low poly cars, so I just made a parking lot.
I increased the chase radius so the one at the bottom on the left will actually start chasing the player from the beginning, but can’t get through the wall. This means by the time the player gets to the edge of the wall to shoot the one they can see, the other one will come around the corner.
I also messed with the movements speed of both the player and the creatures and tweaked their health/damage a bit. It’s still very easy to get through the level, but (just like Rick’s) if I limit ammo it should feel more difficult.
I may also add an enemy ability later which triggers when there’s an engaged enemy nearby, so that if you shoot one, you engage all of the ones in that area instead of just the one you shot.