Airport express with double NAT is super slow
I've had better luck with configuring AAEs when using the older airport utility 5.6 via Macbook - if you're using the iPad to manage setup, it's likely that you're on a newer version of AirPort Utility.   The newer versions are simplified and probably best for the most.  However, it's actually more difficult when stepping outside the  default config settings.  

tl;dr if there's anyway you can manage your AAE via Macbook, then try installing a previous version of the aiport setup utility  &amp; things will make more sense.  (I know this sounds vague, but it's worked for me - more than once!)  [http://support.apple.com/downloads/DL1536/en_US/AirPortUtility5.6.1.dmg