This modifies the $query_args object (rather than replacing it, which removes all the settings that are already in the object created by S&F).

filter-sf-pro-query.php

<?php

function hck_filter_taxonomy_archives( $query_args, $sfid ) {
	
	if( $sfid == 509 ) {
		$query_args['post_type'] = 'articles';
	}
	
	return $query_args;
}
add_filter( 'sf_edit_query_args', 'hck_filter_taxonomy_archives', 20, 2 );

?>