DMZ doesn't magically open ports for 2 network adapters,
only one. DMZ should pass (open) all traffic for only ONE IP address (let say 172.16.20.203), and that should be configured on your router (check there what IP you assigned as DMZ). Then I assume 172.16.20.205 is the IP from your second adapter. HFS perhaps is 'switching' to your second adapter (and that's why it fails on being reachable from the outside).
You need to choose (select) in HFS the IP assigned as DMZ (in your case, I guess is 172.16.20.203). If that fails, then your last option is making a 'bridge' between your 2 network adapters on Windows. You can follow
THIS steps to make the bridge, but I can't guarantee it will work (you have to test it). Versions of "
HFS SSL by SilentPliz" were based on the development of
HFS 2.3x (which was discontinued), that's why if some bug arises, we all depend on the community collaboration to make fixes.
That said, try making a 'bridge' between your 2 network adapters and please comment here if it worked or not.