Nokia Lumia 920
Sweet spot is immediately under the rear camera lens. Ring must be oriented such that it is perpendicular to the silver bar (i.e., makes a cross with it).
Have not yet tested with a case since I do not have one, however it does read from ~1cm away through the air, and it reads through a thin layer of cardboard (at the very least) as well.
Hi @nickh, would you be able to do us a picture of the rear of the phone with the sweet spot marked? We'll add it to the sweet spot thread.
I was actually just working on that. You can see the sweet spot, and the correct ring orientation here. The orientation is critical for getting it to read on this device.
I should also mention that this test was with the V1NTAGE ring, not the alpha.