When the Lakers switch Bryant on Bibby why isn't there a mismatch at the two for Sac?

Is it just having help or semi-zone D with Shaq in the middle prevent Doug Christie versus a point guard midget mismatches? It seems like if that's what it takes to shut down Bibby, the Lakers should do it all the time and just with Kobe and someone as a stopper on Bibby or Kobe as the stopper on Bibby and another 2 and let Kobe bring the ball up.