Flat reflective surfaces act like a mirror, reflecting the light beam pretty much straight. I prefer diffuse reflection. I don't care if hotspot was the right terminology, I got more burning with flat than not flat.Maybe it reflects less light or makes it less intense, just don't care. It works better for me so I use it. Also don't care what other people do. I don't get paid to promote crinkled mylar. I said I do it myself, because people could see in the pic that it was crinkled, so I explained why it looked like that. I'm not trying to prove that it's better scientifically. It's just what I personally like to do. Is that acceptable to you or do I have to leave it flat?