If you have a space that is "longer" in one direction, you should put them along the longest axes, close to the edge of your space. In your example between 0-5, 2-7, 3-6 and 1-4.
If you don't mind anchors in the middle of the floor, you could add them on the center of the walls (2-7-3-6 and 0-1-5-4), the ceiling and floor.
You can try to add one anchor at a time to see how many you need. It might for instance be enough to add two anchors on the floor (easier than in the ceiling).