Looking at the code in Wayfinder, I'm not sure this property is used to include
additional elements? It appears to me that this will limit the results to 17,18,19,20, if 17,18,19,20 appear in the original dataset.
/* if set, limit results to specific resources */
if (!empty($this->_config['includeDocs'])) {
$c->where(array('modResource.id:IN' => explode(',',$this->_config['includeDocs'])));
}
Only those resources which are in both are returned. I might be wrong, as this was just a quick glance, but this would explain it.