I don't think I said anything about the distribution of PAR readings top to bottom. You can't control that distribution, other than by raising or lowering the light. The higher the light is raised, the less variation in PAR from top to bottom. But, as you raise it, the PAR drops everywhere in the tank. With the light right at the top of the tank, it will always have high light intensity at the surface, unless it has far too low intensity at the substrate. I'm still thinking about that subject. The more I think about it the better I like the idea of pendant lights.
But, in general, low light is in the neighborhood of 40 -50 PAR units, medium is in the neighborhood of 50-100 PAR units, and high light is more than 100 PAR units. Different people have different ideas about what those values should be, so those are just mine, for the moment.