I do not understand the point of passive backswing.
Let's share some experiences, please see Date vs Venus in Wimbledon 2011 highlight.
's backswings on both BH and FH, she has racket head down+short backswing, and non-loop swing. Kimiko Date, the former world no. 5, retired and came back, now she is 42 years old.
Her swings are suit for her game, she takes the ball early and hit rising balls very well.
's BH backswing, she has racket head down+long backswing, non-loop swing. She can hit very hard.
Racket head up backswing + Loop swing is not suit for me(I had tried, may be playing once a week was not enough).
I use racket head down backswing, non-loop swing on both BH & FH :
● Behind the base line → take long backswing(like Venus).
● Inside the court → take short backswing(like Date).
My opinions in racket head down backswing + non-loop swing
● Easy to setup backswing.
● Short backswing can hit rising ball easier.
● Response to speed ball quite well.
● Less power shots.
● Short backswing can be read racket face(to predict shot direction).
● Easy to be read shot type,
- top spin → racket head down,
- under spin → racket head up.