You can see how Sam did so well in doubles. If the returner isn't used to a decent kick serve they're just focusing on getting it back in court, which often means the ball isn't directed well, allowing Julia to smack the ball for a winner a fair amount of the time.
Ashleigh Barty|Jarmila Gajdosova|Casey Dellacqua
Li Na|Svetlana Kuznetsova|Vera Zvonareva|Francesca Schiavone
Stanislas Wawrinka|Ryan Harrison|Andy Murray
I wonder whether Sam has deliberately changed her toss and/or service action. When she gets hold of it it looks pretty potent atm, but I can't remember seeing her drag so many serves down so they hit the net only halfway up to the tape.