For tricky setups that require your short url to reside in a different location than your yourls installation
define( 'YOURLS_SHORT_URL', 'http://shorturl.com' );
You need to direct traffic from your defined short url to your yourls installation. To do this, create (or modify) an .htaccess file in the directory you defined as your YOURLS_SHORT_URL with the following:
RewriteEngine On
RewriteBase /
# BEGIN YOURLS
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([0-9A-Za-z]+)/?$ http://shorturl.com/yourls/yourls-go.php?id=$1 [L]
RewriteRule ^([0-9A-Za-z]+)\+/?$ http://shorturl.com/yourls/yourls-infos.php?id=$1 [L]
RewriteRule ^([0-9A-Za-z]+)\+all/?$ http://shorturl.com/yourls/yourls-infos.php?id=$1&all=1 [L]
# END YOURLS
.htaccess is tricky and everyon's setup will be slightly different so that part is on you. Otherwise, feel free to submit problems feature requests using the GitHub issue tracker
developed by @gerbz