Experiencing some rather dramatic discrepancy in MeshFilter and MeshCollider "sizing" of an imported sphere. The MeshCollider was added after import Component > MeshCollider. How do you minimize this discrepancy?
You make sure you don't have any vertices hanging out that aren't part of the sphere. I tested this extensively and never had a problem:
http://www.unifycommunity.com/wiki/index.php?title=Mesh2Collider