a few things to note:
1. LSWS Stand Edition only reads up to 5 vhosts from Apache httpd.conf. If you have more vhosts than that, you will be unable to server others vhosts.
2. make sure LSWS listener is on 127.0.0.1:8081 (or any IP:8081).
3. _SERVER['SERVER_PORT'] is PHP environment variable. in your case, it will reflect the port backend server LSWS listens on (i.e., 8081).