Nodes are too far apart force directed layout.. How can I get them to cluster?

[yohda]

http://www.yohman.com/maptwitter/json/proto.html?id=28

In my example above, the big nodes have connections to other nodes positioned far apart.  Even if I drag the big nodes, the connected nodes do not follow it. Is it possible to have them cluster closer to each other?

Thanks in advance!