I'm not sure why, but I've always thought it interesting that radiation scales as a fourth power. It's unusual to see forth power relationships in fundamental scientific processes.
Most materials scale with T^4. You would need a very weird radiance spectrum to do anything different.
That said, we are talking about something that has a weird radiance spectrum as a selling point, so, expect some deviation from the standard T^4 curve.
1) Does it emit more IR at higher temperatures? In other words, would pumping hot water through/under it produce larger temperature drops?
2) Is it weather proof, or do you still need to find a coating that protects it while not blocking the IR?