Again, my search was avid and i couldnt find anything on this.
It seems the Hunter has some kind of 'aura' around it that blocks the operatives L.O.S.
Look at this:
To look at it, it looks like a reasonably clear L.O.S. and now ill move the hunter to one side:
and the shot opens up, yet if i now move the target cursor to the square just adjacent and behind the alien:
the L.O.S. closes again - although by looking at the screen it looks like a reasonably clear shot.
This is easy to replicate.
Apologies if this has already come up.