Sony Xperia XA1 Plus works perfectly with the HF side of the NExT.
While I tend to center the NFC Forum logo for regular tags, the best performance with x-series implants seem to be achieved if you go above the NFC Forum logo, around the same level as the LED.
You’ll want to make sure that x-series chip will end up being vertical to ensure good coupling, which means that it will look something like this:
(Only tested without a case.)