Hello Jason,
Thank you for contacting us.
I would also recommend to have a look at instance-level IPs, which will make the passive FTP able to use the full port range:
https://gist.github.com/nmackenzie/db9a4b7abdee2760dba8
http://blogs.msdn.com/b/cloud_solution_architect/archive/2015/05/05/creating-azure-vms-with-arm-powershell-cmdlets.aspx
Please let me know if you have any queries.
Regards,
Dipin Mathew.