Hi,
To display results that match at least one chosen tag is possible. If you use taxonomy terms then changing this option, for other taxonomy terms changing this option will force that logic.
However the final logic would be:
( Child-1-of A OR Child-2-of-A OR Child-3-of-B OR Child-4-of-B OR Child-1-of-C )
and not:
( (Child-1-of A OR Child-2-of-A) AND (Child-3-of-B Child-4-of-B) AND (Child-1-of-C) )
This only works for separate taxonomies. Each group between the ‘AND’ operators has to be in a separate taxonomy in order to achieve this.