I usually get a "ring" when reducing, figure it's a combination of particulates, flavor and gunk. Some tobaccos leave a well defined ring while others are virtually ring-less. Never had (or at least noticed), sugars separating during the reduction, but certainly wouldn't mind if they did. I'm pretty sure the casings used on the aromatics I'm extracting are loaded with it.
I have been reducing at room temperature by replacing the mason jar lid with a disc of 5um felt. With the extended reduction time I am getting globules (oil?) congealing and sinking to the bottom of the jar. I am also getting an oily substance adhering to the sides of the jar. When I can no longer smell alcohol, I slowly transfer the extract to a beaker using a spatula to keep (most of) the oil in the extraction jar.
At this point, I add enough PG to result in a final volume that is equal to the volume that I would have ended up with doing a PG extraction. I am doing this for a few reasons. For one it enables me to do an apples-to-apples comparison to my PG extractions (gunk factor, flavor, extract %'s, etc.). I think PG will act as a preservative and keep longer. I think it also reduces steeping (aging) time of final mix. The last reason (which may be overkill) is I am doing a final filtration after adding PG, and I would rather lose a few ml of diluted extract rather than concentrated extract.