I don’t know the answer to this, my guess would be placed in whatever orientation they come.
My reason for this guess, I shouldn’t really matter which orientation they have in your hand.
What side of my NExTis the LF - xEM and HF - xNT?
I haven’t tested this an is purely theoretical ( I am expecting somebody to pull this apart ) but here goes anyway.
Looking at the below ( Speculation )
LF on the Left / HF on the Right ( Looks like longer antenna winding on the left one, therefore LF )
I assume you didn’t look at your NExT before or when you implanted it.
The LF should have a longer read range BUT, It is really going to depend on the reader you use. I would recommend a Proxmark because you can have measured results.
Do you have access to Foil tape, otherwise some tinfoil and tape may do it.
Locate your NExT, do a read of both HF / LF with Proxmark, Record the results.
Then cover 67% of the implant with the Foil, and try a read,
Note the end and result figures, Then cover the other half and repeat.
Compare the results, and you SHOULD HOPEFULLY be able to work it out.
I can’t guarantee this will work, but it would be my first attempt to work it out