Where is the NFC element located in a Moto X? I have a Moto X (2013 version) -- and use Google Wallet's tap-to-pay at merchants that support it.  With certain readers, I end up moving the phone around over the reader until it works; knowing where the element is might make it easier to line it up correctly on the first try.
You can check iFixit Moto X Teardown. Looks like it takes up most of the center of the back.