Hmm, ok.
Inline editing like the news articles module does is not very common for dotnetnuke modules.
99% does editing in the edit skin you set.

You can set the editor width for Ventrian.
Admin options > Main options > Form settings.
Try setting the editor width to 300px, you will see that the rest will still be to wide.
The title input itself is set to width:350px for instance.

I think the only solution is to choose a pane that's wide enough to put the module in.