Thanks for spending your time to do these tests. Do you still have the two small pieces of foam set up with your meter mounted to try one more test? Could you scuff the surface of another piece of foam with sandpaper so it takes some of the sheen off the surface of the foam, then test to see if that makes much difference? Try a fine grit paper.
Sure I can do that. I'll also try the test I already did but with a little bit more accuracy as to the angle between the two lights instead of just guessing the angle I am holding it at.