Where in the Nexus 4 is the wire wireless charging coil?

I've just received a "smartfox qi " wireless charger as a gift, but it won't charge my Nexus 4 despite its indicator light turning on, and the Nexus 4 says "charging wireless". Still, it doesn't charge, the battery graph shows a power depletion just as if it were just lying on a desk. It's running stock 4.2.2 without a case. The charger has the exact same dimensions as the Nexus 4, so I just placed it exactly on top. I'm thinking that the wireless coils didn't match up well enough. So my question is: **Where in the Nexus 4 are those charging coils? How do I have to place it to ensure maximum-efficiency charging?** *Bonus questions:* 1. Wireless charging heats up the Nexus 4 a lot. Is this really healthy? Won't it significantly reduce the lifetime of the (non-replaceable!) Nexus 4 battery? 1. What specific product would be a good recommendation, specifically for the Nexus 4?