If you want the algorithm to consider two or more classes as a single class without merging them, you can use links. To create a link, select the Master Tab, select a class and click on the big red point (part A in the following figure) on the top of the red arrow.

Dragging to create a link

    Then drag the line to the class you want to link with and drop it. A link will be created. In the following figure, you can see two links. The blue one joins the first and the third class, and the green one the fourth and the fifth class.

Two links

    To remove a link, select a linked class and hit the Remove Link button. You can merge a link into one single class if the link covers two or more adjacent classes by hitting the Join Link button. If this is not the case (i.e., if the classes are not adjacent), you have to first use the reorder mode to make the linked classes adjacent.