I just switched to the Oval ring today, but for those who are wondering how oval it is... this is your thread. Now the ring I use is 1 3/4'' inches, but I was assume the same will be true for all sizes. Mature Metal does their ring sizes in 1/8'' inches and it would appear the Oval Ring is indented by this amount. They also use 1/4'' steel to make the rings I believe. Here function I built on a math program that should show you the difference in sizes. https://www.desmos.com/calculator/vapb6y2xtp If this is not correct please let me know and I will update the program to show the correct formulas.
Oh, they are all wider than they are tall like in the program. I am sure you could ask for it the other way, but I can't see that being very comfortable.
The picture below shows the difference between an Oval vs a Round in a 1 3/4'' Diameter side by side.