I´ve tried to change the attribute Size/Width in properties of screen section (F4), but the width in app is still the same.
Size-Width changes the size of the widget in the detail view. In order to set a default width of a column in a table view you need to set GridColumnWidth property.
One more thing: The GridColumnWidth property only works as a default width. Once the user resizes the columns in his application with his mouse these widths are saved in user settings and are used next time. The default setting is then ignored.
GridColumnWidth is full property name.
Thanks @Kit4it, updated the original answer.