Interesting you you rate the sea & sea optical glass as one of the best domes, isn't this only about 6-7" diameter? I have read the large sea & sea fisheye dome is optically better than their glass offering. I do prefer glass domes though for durability. I did plan to get a zen 9" dome and an adapter made for my sea and sea rig but on arrival of the sea&sea fisheye dome I was quite impressed so it would be silly not to give it a good trial hence asking the questions here
I have the large Sea & Sea acyllic dome and it is one of the best but, with the Tokina, the smaller optical glass dome excels. Can't tell you why. Maybe it's the perfection of the curve or the position of the lens node or both.