Aaaahhhh-the difference between an engineer and a physicist:

engineers toast themselves for a 50% improvement.

Physicists ignore less than an order of magnitude delta as "statistics".

Waldo's on the right track. I made these same measurements (on my N/A) 5-6 years ago.

Same results. Look it up. The heatsoak the SC guys observe is a bit more problematic-more mass to hold more energy (heat).

And how to remove it.

JEFASOLD-polishing the exterior of the aluminum pipes gains little. It may make them reflect visible light better, but has little effect on infrared. It's a wavelength thing. That's why that neat gold-faced NASA stuff I used is so cool: 97.2% reflection. And a really thin (.005") fiberglass matt inside.

Waldo's also corect in that the only true measure of the insulated pipe vs. uninsulated is a tc in the airflow.

4 of them: one each in the input ends and one each in the output ends. measure delta T and contemplate.

Nice work Professor. You must be one of the 5%. I work with them. This is the figure I came up with that reflects how many are with a pinch of ****.