How to tighten the AMCL particle swarm envelope ?

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Looking to tighten the envelope for the ensemble of points placed by AMCL, the topic is /particlecloud. I'm finding that I don't need to worry about the 'kidnapped robot problem', where the robot could suddenly be taken to any point on my map and the envelope stretches and randomly places estimates all over the map.

I'm driving my robot around by either teleop or 2D Nav Goal in rviz and the distribution of points shouldn't be moving further than something like a 2x2 m^2 radius.

Does anyone know the input parameter to amcl that can reduce the covariance? of particle swarm?

Thanks!