The Variable Strings tab lets you specify how many strings each stage will have.

 

This is the General match properties screen, after I've set stage 9 to have 3 strings and have saved and reopened the match definition.  Notice that the Strings per Stage entry shows 3, and is greyed out (disabled) because I've clicked Variable.  The disabled area will show the highest number of strings for any stage in this match.  If any stage has more than 4 stages, the program will use the smaller match data entry screen, just as it does for Classifier matches.