I guess it depends on how you take what he wrote.
"The total light incident on the three different areas 3’ X 3’ ft, 2’ X 2’ and 1’ X 1’ at 6” from the lamp using a flat sheet reflector with white paint..."
I look at a DIY reflector as being a flat sheet reflector made out of aluminum flashing. If you search around and I'm sure you can find tests which show the difference in reflectability between flashing and white paint. Neither is very good compared to any of the engineered reflectors Sanjay tested....which is my point.
Even if you make your own from whatever scrap aluminum you have laying around, you still need to buy a mogul base and a bracket to mount it to the reflector. You can buy an engineered reflector with the mogul base for $30. Seems like a no brainer to me .