Hi,
Well, the only way to do that is via custom coding, instead of using the advanced field, as there is no parameter to control that.
I constructed a custom code for you, which should help with that. Try adding it to functions.php in your theme/child theme directory. Before editing, please make sure to have a full site back-up just in case!
Change the $custom_field and $length variables according to your needs.
add_filter( 'asp_results', 'asp_c_field_to_desc', 10, 1 );
function asp_c_field_to_desc( $results ) {
$custom_field = "field_name";
$length = 100;
// ------ DO NOT CHANGE BELOW ----------
foreach ($results as $k=>&$r) {
if ($r->content_type != "pagepost") continue;
if ( function_exists('get_field') )
$meta_value = get_field( $custom_field, $id, true ); // ACF support
else
$meta_value = get_post_meta( $id, $custom_field, true );
// Modify the post title to add the meta value
if ( !empty($meta_value) ) {
$r->content .= wd_substr_at_word($meta_value, $length);
}
}
return $results;
}