Update! I made the 4 hour round trip to my nearest store. The S was too tight (as I suspected it would be). I ended up going with the M - it’s a hair bigger than my Loves so I’m expecting a bit of overlap/movement if I stack but it was so absolutely stunning I couldn’t leave it there. And yes, there’s variation in the sizing. I tried another M (they only had 2 in yellow gold) and it was bigger in circumference and the head/tail overlapped less. This M is about 6.4 inches inside circumference.
I can’t even capture how amazing it is in a pic. So shiny and sparklie!
thanks to all who helped me!