I suggested that it would be nice to set the width of the user defined fields:
But the ideal would be an interface that let you drag and drop the fields, so you could place one between existing lines, or place them side by side on the same line. The text entry fields work well when their entire contents can't be viewed, so there's no reason that they couldn't be jammed together if the user wanted. This type of drag-and-drop configuration is fairly common in Windows applications and is even becoming fairly common in browser-based web applications.