E represents the guard.
E to p-1 represents the limits of peripheral vision, side to side, in the "eyes forward" position.
E to p-2 represents the limiits of peripheral vision, side to side, when the eyes are turned to the left or right and the head kept still.
f-1 (the inner yellow section) is the boundry of the field of view of the ground around the feet when the eyes are looking straight.
f-2 (the outer yellow section) is the boundries of the field of view on the ground around the feet when the eyes move but the head doesn't
It is interesting to note that it is impossible to see your feet if your eyes are looking straight ahead.

Looking at the diagram you see that the guard is facing forward with his eyes aimed straight ahead
The wall behind him represents the limits of peripheral vision. The key here is that his attention is focused in front of him.
The angle of the walls represents the degree of vision of the guard when he moves his eyes left or right without turning his head.
The yellow section shows the limits of peripheral vision around the area of the feet.
The white circle represents the "eyes forward" range.
The yellow section inside the white circle show the limits when he looks down without moving his head
It should be remembered that all movements that are done behind the guard MUST be silent, since any noise may attract his attention. (A good timie to do this is when he is shooting or shouting)