No more horizontal shadow and the facets are on/off instead of all on or off. Moral of the story: Try more than one ring of similar specs. Diamonds are finicky!
Great! It is lovely. I'm so glad you were able to resolve it with them.
So, it was the cut of the stone, after all. Very interesting (and sadly pathetic) that Tiffany would offer up an EC with poor faceting and light return at their price points.