Sorry this took so long, the sweetspot on my Note4 is right around here shown in the image below.
I've been blown away by how good the antenna matching is with this device actually. It picks up the rings from nearly a centimetre away without a case on and works flawlessy with a thin case on - one of those silicon/plastic wraps that have a type of covered card on, that folds over the phone. Constantly amazed by how good it is!