I can't answer your question, but please allow me to point out the cell phones are radio devices. Metal is a conductor, and therefore affects radio waves. Sheets of metal tend to reflect radio waves. Replacing a non-metalic cell phone back with a metallic back will affect the phone's radio (cell, LTE, WiFi, and Bluetooth) performance -- possibly improving things, but far more likely causing connectivity problems. Plus, there's a good chance it will increase the amount of RF energy leaving the face of the phone.
Something to think about with phone backs, cases, docks, stands, and car supports.