That's a good question. There's other pressure points as well
  that should work just as well. For me, massaging between the
  thumb/finger worked just as well and it's more accessible.

  But yeah, that's a very good question. I mean you *should* be
  able to access the muscle to get the knot out ; maybe you could
  go at it from the opposite:

  push your chest forward and shoulders back. then pull your
  elbows straight down as if you were trying to shoot an aircraft
  out of the sky with your chest.

  [best way I can think of to describe the movement]

  It's a stretch that seems to unravel the knot in that muscle
  spot, at least for me.