I ran into an issue today on the vagrant IonicBox when I tried to create a new Ionic project at work behind the firewall/proxy even with all of the configurations for npm, git, bower, and bash setup for the proxy as detailed at proxy-configurations.
Luckily, Ionic had a fix for this already.
All I had to do was put PROXY=http://myserver:myport in front of the ionic start command.
PROXY=http://myserver:myport ionic start todo blank
All I had to do was set the http_proxy environment variable and then run the ionic start command as I normally would.
ionic start todo blank