Lowering the Fastbreak slider to 30 doesn't stop the CPU from running the fastbreak, it just stops them from always putting a quick shot up, even if the defense is set and right in their face.
If you want the team to be more aggressive on the fastbreak, bump them up 5 points or so. Or you could leave it at 100 and see how that works for you, but I'm guessing that they will always force up a shot regardless of the defense.