Yeah, I've never seen anybody do it exactly like I am. Some pretty close, but not the same way. The insulation is mostly to keep heat out in the summer. I have insulation on the ceiling already to keep the heat in come winter. I was thrown a curve ball when I found out the recommend screwing it down every 2 feet. I'd planned on 4. Not a big deal though.
Look into your colors of metal roofing if you want to stop heat. Told to me by a old friend years ago red is the worst color to get to absorb heat so its also the best for reflecting heat...