I'm new to all this, but looking at all the Semi-state brackets, it looks like they just pick a regional to start with, line them up against another regional at 106 and let the placing do its thing within the bracket. Then they move on to 113 and give them a different regional; wash, rinse, repeat up to 285. The only real question is which regional you're going to get paired with at your weight, and I'm guessing they keep quiet about that ahead of time to try and keep the integrity of the regionals in tact (i.e. keep kids from trying to game their placement in regionals to get a more favorable matchup).
But like I said, I'm pretty new to this; that's just what I see when I look at the brackets.