How to change the Height in Fan Module?

Holger,
Unfortunately, this is a limitation of the Facebook Fan widget. The stream height is fixed. The only thing that actually 'grows' is the height of the faces area. So, if you enable Faces, you'll see the whole module grow to show a lot of faces. The stream area will still be the same size though.

You can test, and see, this limitation on Facebook's own configuration tool below:
developers.facebook.com/docs/reference/plugins/like-box/
Set the height to 1000 and then enable/disable the faces and the issue should be very clear.

Unfortunately, this is a limitation that we can't get around.

Hope that helps explain, and good luck,
Alex