I have been working with my ring for a couple of months now.
The phone is a Google Play edition S4. Model GT-I9505G with stock Samsung Battery.
Without any case on the back, the phone sees the ring in a very small sweetspot.
With ANY case on the phone, it does not see the ring at all. I have worked with this for quite a while, very patiently.
Cases I have tried:
Samsung folio case.
Spigen Slim Armor.
So, I will be returning this ring. I really wish this worked, and if there is a version of the ring that works for this phone through decent cases, I would be happy to try it.