You can allow group sizes of 1 or 2 studs - any group sizes that you don't want to be considered can be excluded.
For example, if you do not set up groups with 2 studs, then in auto-design the program will only try to achieve a successful design with a maximum of 1 stud in a group.
For groups with 2 studs you must specify the pattern to be adopted (e.g. along the beam, across the beam, or staggered).
Note: It is up to you to check that a particular pattern fits within the confines of the rib and beam flange since Tekla Structural Designer will draw it (and use it in design) anyway.