I know it still works through a case, but does Samsung Pay work with a popsocket on the back? I don't know where exactly the sensor is inside the phone. Does the phone just need to be within a few inches of the keypad to be recognized?
I've seen it work, and it usually works within an inch or so apart, but it also depends on the terminal (some really need you to press the phone in the right spot). MST and Wireless Charging coil are near the center of the back plate.