try thinking about bending the bar, while squeezing, rather than puling it apart. I find the bending idea effective.
ALSO SCOTT SAYS TO Pull your feet back so you're pushing from the BALLS (of the feet). USAPL doesn't allow this, they officially demand a flat-footed position.
J.M. Blakely's super tape also advocates balls of feet. When will USAPL catch on?