Those diagrams are a joke. Do you guys have any understanding of the physics of light and of basic geometry and trigonometry? First, read up on what a parabola does. Second, understand that when light reflects of an object, the angle of incidence = the angle of reflection. In other words, the pool ball comes off the cushion at the same angle as it hits it. Few if any rays will ever leave the arc tube, pass through the glass of the bulb, hit the reflector and return to the arc tube. And we already covered the additional area issue.
As for plant shading - yes, if you have a few small, sparsely grown plants inside a room covered in Mylar and in pots you can turn, you can manage to get light to all sides. But assuming you are doing a dense grow, with bushy plants, this will never happen. Light simply does not penetrate through one side of a bush through to the other with any appreciable brightness. And the stems will not make a 180 degree turn and grow to the front of the plant.
Really, I don't see why this is so hard to comprehend - it is not rocket science. Get yourself a cone shaped cup or an ice cream cone and shine a flashlight straight down on top of it. You will notice the whole cone illuminated 360 deg around with only the area underneath shaded. Then shine the flashlight from the side and look at the opposite side. Notice that a full 50% is shaded.
Now sure, when you grow 5-10 scrawny plants around a 600W HPS, light will make it through to the back side. Try growing 24-36 plants under a single 600W HPS and see if any light gets through.
Fact is, branches grow laterally 360 deg around the plant, not 180 deg toward the side your light is on. Top lighting lights the plant 360 deg around, side lighting only 180 deg. If you have a thick canopy, 50% of your plant will receive no light. There is no two ways about it.
Have a look at this:
http://www.adjustawings.com/index.htm