This is definitely true for his BH slices in general, but his BH slice drop shots go ~90% to the opponent's deuce court.
He follows a familiar pattern with his BH slice drop shots. It usually follows a deep crosscourt BH topspin, inside-out FH, or big kick serve which pulls his opponent wide and deep on their ad side. Then, with their deuce side wide open, he hits the short dropper. Sweet!
I've been working to incorporate this pattern into my own play, it can be deadly if you can disguise the dropshot with the racket prep of your normal BH. Fed has incredible disguise, it's rare that someone reads his BH dropper!