/**
 * Implements hook_query_TAG_alter().
 *
 * Favor exact matches and shorter matches in node reference
 * autocomplete.
 */
function mymodule_query_entity_query_node_alter(AlterableInterface $query) {
  if ($selection = $query->getMetaData('entity_reference_selection_handler') && $query->getMetaData('entity_type') == 'node') {
    $query->addExpression('CHAR_LENGTH(node_field_data.title)', 'shortest');
    $query->groupBy('shortest');
    $query->orderBy('shortest');
  }
}