Painting the Safe Ground

What: All of this is invisible in play. There is a number on the screen, but nothing says why one corner keeps a character alive and half a step to the left does not. So I painted it on the floor. My first plan was to draw lines out from the character's eyes and stop each one at the first thing it hit. It was the obvious approach and it did not work. A character crouched tight behind a low wall is hidden. The same character standing further back along that line is visible over the top of it. It asks the question about every patch of ground in range: would somebody standing there be visible from these eyes, and would somebody crouching there be visible. The floor gets painted with the answers. Amber means standing there is enough to be seen, orange means even crouching does not help, and shadow means the ground is genuinely out of sight. This is a tool for me rather than something that will ship.

Why: I cannot make the cover rules feel right until I can see where they go wrong.