Latest build release now has a Search Operator parameter under Parameters > Search of your fieldgroup field. You can now control specifically how it searches when more than 1 field is selected. By default it will now try to match your userlist (simple any = OR, simple is = AND, advanced = OR), but you can specifically set it to OR/AND from that parameter. So for your usage you'd either leave it as is if your userlist is set to simple is or set it to AND.