If they are actually touching then they are too close. The xenia cannot sting the anemone.. but the anemone can sting a xenia.. or so they say.
I happen to have a rock with xenia on it and my BTA decided he wants to live ON that rock and cover the xenia completely, I figured the xenia would die off but whenever the anemone shrivels up.. there they are
pulsing and happy. I know that its not touching the anemones stingers while being under it.. but its still interesting. I've actually had my BTA touch a few coral and not kill them or cause any noticable damage.. its still not a good idea to keep any coral or anemone touching another coral or anemone though - as a rule of thumb.