Could you please give more information on the version you are using?
ip_webserver is kind of old - outdated, not used any more. You might still have it in your Settings.cfg file... but it's not used in current source code.
The other two settings are used, though. And I have no reports (other than yours) about them not working... Did you add them manually (then they are - wild guess - not supported) or were they added by PlexConnect and you just changed there value (then it should work...).
You might want to attach the complete Settings file, plus a log of a PlexConnect startup.