NFC sensor/detector on Axon 7 mini

[M01684340561220]

I am using this device since Feb 28 of 2019. I have setup G Pay on it. I have experienced that bottom side of the phone does not function at merchants POS machines rather screen side of it functions and payment goes through so every time I use GPay I flip the phone otherwise it does not go through. Is it normal. What is the reason for this. Usually in videos and other instructions it is shown to use the phone with screen up and finger print sensor side on the POS payment machine.