Disable Internet Access to ECP

When I follow this article to disable ECP access from the internet, ECP access then no longer works from the server directly via the internal URL say (https://servername/ecp) what's the deal? This isn't a valid solution. I need to disable ECP access to the public internet but still obviously be able to manage my servers internally, how is this done?

http://technet.microsoft.com/en-us/library/jj218639%28v=exchg.150%29.aspx