I do think that the ring size is part of the problem, but I am not convinced it is the entire problem because I have to pull the eternity band down so tightly over my finger with a Snuggie that it cannot be removed in order to have it sit under the head of the solitaire. Here is the CAD image I received... I had a complete panic attack when I saw this, which I expressed in email saying "The way it looks right now, I would never wear it for fear of it damaging my solitaire." This was followed up by a one-hour conversation with the jewelry designer because I was so concerned. I was told that CAD "appear a little sharp in the edges and bulkier than the finished product" and that the eternity band would not touch my prongs. I guess it is my fault for believing that, because the CAD rendering is pretty much exactly what I got.
And regarding the ring size... There was actually a comedy of errors with this. I had ordered the eternity band in a 5.5 and the solitaire in a 5, but the instructions that were given to the designer erroneously had both rings as 5.5. So he designed these rings not knowing they were supposed to be different sizes, and perhaps that is part of the the problem as well. If he had known the eternity band was going to be bigger, I would imagine that he would have explained to me about the rubbing. Any seasoned jewelry designer should know this and when your client is completely paranoid about rings damaging each other, this would be crucial to point out.
I'm not sure what Tiffany's has to do with ordering custom rings designed to fit perfectly together? Tiffany's was simply my inspiration for the rings. I wanted to have my rings made together to ensure a perfect fit that would avoid this exact situation I am dealing with now.
CAD Rendering