Hi Hugh,
Interesting. This cross section through the coma appears to show a different story to this vertical section.
https://britastro.org/comment/8942#comment-8942
Perhaps there could be some directional effects in the differences between Dust,Na D and other emission bands with the gas emission moving off the slit to the left relative to the dust. I have some cross sections across the tail still to analyse which might shed more light.
Cheers
Robin