Port-forwarding on Android 2.3.6 wifi-tether using Port Forwarder app
I am not sure which version you're running, here is my advice. The cause you're probably blocked, is due Android's firewall and strong Se-Linux policy. 

Since you have a full root access, you can get a shell with ADB, and check that. Type su - and it will get you into root. I am using TerminalEmulator, but you can use native one, if it is shipped with OS.

If I've understood you correctly, your phone acts like router in tethering mode. So this is needed to forward packets:
echo 1 &gt; /proc/sys/net/ipv4/ip_forward

See if that helps. Most likely, you'll need to play with iptables, allow port 80,443 on the tethering port. 
This is not complete answer, but it is too long to post as a comment.