Hi Smithy,
I tried the thin walls option, but did not notice a difference. To remove the thin edges, I scaled the height from 6 mm to 8mm, 9mm and 10 mm, removing the tops and bottoms, leaving just 6 mm in height with edges around 1 mm. Each print reached 5.5mm.
I noticed some asymmetry and it appears some of the lower layers are lost, so I printed using a raft, and the entire ring printed in full height, and with symmetry.
-Christian