Thank you very much @eKretz those are enlightening images, and very low noise, as expected. To further illustrate the point, and provide comparison, I present a couple shots from my Seek Pro a few minutes after capturing a fresh NUC and no smoothing. No kid butts here but I do have plenty of tabletop clutter. The first image is with the grayscale palette autoranged and yielding an 8.9° F range. With the exception of the uncorrected bias-changed pixels (bright white) this looks to me about the same noise level displayed in the E40 image with 3.5 degree span. The second image is with the grayscale palette set for 80 shades per degree, yielding a 3.2°F span and you can see much more noise; even more noise than in the rainbow E40 shot. I'm not sure about the Pro, but the Seek XR aperture is F/1.4. The aperture opening is the same on the Pro but I have not bothered to calculate the focal length.
I like using grayscale for comparison because I long ago determined that my eyes can only distinguish (at best) 32 shades of gray. So, for instance, if the palette is spread evenly over a 3.2 degree range I can expect to see differences of 0.1 degree. I see just a tiny bit of graininess in that E40 shot with the 3.5°F span so I would call it about 60mK (and according to FLIR's site it was spec'd at < .07C sensitivity, so, about right!). Blowing up & comparing with my Seek shot with 8.9° F range the noise is a bit more pronounced so I would call it over 150mK (but it also is spec'd at "< .07C" sensitivity, so noise exceeds sensitivity).
The whole point of this is that you can't properly compare the noise of one camera with another unless you know enough about the palette & how it is applied to the temperatures. I took the "rain" and "iron" palettes from @frenky's program and started deleting colors until I could see a difference between adjacent colors. I reduced the rain palette to 50 colors and the iron palette to 30 colors. Frenky's rain is similar to the FLIR rainbow palette, so that could explain why @eKretz said the rainbow shows noise worse--because it has more human-recognizable colors than the iron OR grayscale palettes.
So how does this apply to the OP's issue? If you look at those sample images in "Reply #2", the images from the 04 have a span of around 12 degrees and the ones from the 18 have spans of around 7 & 8 degrees; not quite a 2:1 difference. A bit hard to say for sure, but I think they are pretty close to the same noise level.