How would you prove the presence of a state-sponsored firewall?

So here's the situation. We have a data center in Munich that runs a remote desktop gateway server. Users connect via port 443. This works fine for everyone but a single office in Dubai. Once that office gets more than 7 or 8 simultaneous streams connected they begin experiencing extremely poor performance. Remote desktop server is fine and other users connected from other locations at the same time do not experience this issue. Taking packet captures from the Dubai office firewall shows significant packet loss, and new sessions always require 5 retransmissions of the server hello message. The issue persists until that office began using a different RDS server at which point at work fine until again they started using too many simultaneous sessions. We changed the eye peas on the two or DNS servers and again that fix the problem until they used too many sessions again. I'm trying to convince management that this is a issue involving the firewalls responsible for censorship in Dubai. Do you guys know of any ways around the sort of problem or anyways that we can confirm this hypothesis?

Thanks any help is appreciated