Use the default bool parameter of the KeywordGroupSearch command to specify the default boolean connector.

Individual words and phrases can be grouped by parenthesis and connected by "and", "or" and "not" to create boolean expressions to be used in searching an index. Adjacent words within an expression, not connected by "and" or "or" are treated as though they were connected by the default connector, which can be defined as part of the Search Keyword Index Request.

Search index default boolean connector values: