I don't have an S4 but an Z10. From earlier posts in the KS website there was a concern of the normal rings not being able to be read, but mine seems fine, even with a Skinomi skin applied. There is just one spot for it to work but once that spot was located it works fairly stably. So I think this would be similar to S4. @Lokki made a very good suggest of orientating the ring and I think it does matter. Also it might not be as quickly as one would expect, it might take 1-2 second for the device to pick up the signal.
On a different note, I can't find the bonus tags in my package. Is it something only for a specific batch? Should I be contacting the support?