You can use the Patterns page of the Preferences window
to specify the initial shape of collaboration pattern instances on the class
or freeform diagram views.
Before you begin
About this task
The shape of class and package types of pattern instances cannot
be modified.
To specify the shape of collaboration pattern instances
on the drawing surface:
Procedure
Click Window > Preferences, expand Modeling, and click Patterns.
Under Collaboration pattern instance shape,
select one of the following options:
Rounded rectangle: A small and more compact
shape.