It's not that hard to determine the cheaters, They never change direction and find an enemy at the outer edge of their screen. Anytime an enemy is spotted from a change of direction they are always spotted almost dead center screen if not dead center.
After awhile it becomes very obvious of the missing (finding enemies at the outer edge of the screen directly after a direction change) it should happen as often as anything else in the game. But not for cheaters using targeting systems to find most of the enemies, "it rarely ever happens" (every enemy found after a direction change is CENTER SCREEN and never off to the edge of the screen) this is how you spot them.