port forwarding

hi

i have set up a port forwarding role from my router to my web directory of my synology nas.
the entry port is dyndns:57433 then redirects to localadress:80.
this works fine.

but the problem is the wordpress index is located in the subdirectory /wordpress/.

locally it works fine by redirecting to /wordpress/, but from the internet it looses it access, i tried everyting like:

dyndns:57433/wordpress
or
dyndns/wordpress:57433

noting works, any idea?