I think you're misunderstanding him Dave. He's saying that putting the insulation over the tape will make the tape have to work harder to heat the fridge. Of course the probe goes inside the incubator, but he's saying that even with the probe inside of the incubator, with the heat tape having to heat through insulation, the tape is going to heat up beyond what it needs to to warm the incubator, making it potentially dangerous.
Now I don't know anything about radiant insulation, so I don't know if this argument is sound, but it makes sense to me if it's anything like normal insulation. He's meaning to say that because the surface of the radiant insulation won't be as high as the flexwatt, problems could occur. Anywho, I think he was just making a helpful inquiry, and you might have gone off on him a little bit, lol. I dig how the fans look at the bottom there, perfect fit, and I like the idea of having air pass through that gap in the insulation on top and blowing to the bottom, where it could naturally rise. Seems like a cool design to me.
Cheers,
-Matt