Tim Mayotte was a very good player back in the 80's, made SF of Wimbledon, Australia, beat Connors in the Queens Club final, remember he had an epic fie setter with Lendl on grandstand at US Open. Mayotte won 12 singles titles was #7 in the world. He worked at USTA National Center but mysteriously was dropped from that job even though he is an excellent coaching mind.
I think his advices for Harrison here are spot on...
http://www.tennis-prose.com/articles...-fix-his-game/
"If you were to look at the lack of length and the lack of rotation in his backhand, it's not creating nearly the amount of racquet head speed that he's capable of."
There's more but Mayotte I think is right. It's a wonder why his team of coaches in Bradenton have not been able to bolster Harry's backhand. If this kid gets a Safin like backhand, he can be a terror in the ATP.