Really nice to see this.
The comet is approx 30 degrees from the sun, so the background should display Rayleigh scattering induced polarisation of a few percent. From memory, the orientation in the first image looks roughly right given the suns position pretty much below the north horizon. The comet should have its own dust response – as the Zodiacal light does – and certainly appears to here. I’m a bit perplexed by the orientation of the background polarisation in the second image though. Was the amplitude the same?
Your amplitude measure, was that a Stokes parameter or the degree of total linear polarisation or similar?
I imagine perfect alignment of the 4 polariser images is essential to the values measured when the target has fast changes in brightness. I have always had greatest problems getting good results in parts of the image with steep gradients – subpixel registration is important (I found to my cost).
I assume you only used linear polarisers.