Hi.
Here is the reason for the container to behave like it does:
http://vincent.polenordstudio.fr/snap/bd45j.jpg
The container widget only exists because of this reason: Keep the content centered and in the grid.
Now, the container is only a DIV with some settings you can’t change.
So you can build you own container. Start with a div, give it a class like “mycontainer”, set it up for desktop, 960px centered, then continue for tablet the way you want etc.