Hi guys,
I have learned a lot on the topic of deliverability lately, especially in the context of the the Chinese Internet.
To put it simply, you really need to put a CDN in front of S3. It’s dead easy to setup and will do wonders for your deliverability issues (yeah you have some 
). Right now, AFAICT all artefact downloads are served straight from S3 us-east-1. This yields some really bad bandwidth and latency in a lot of corners of the world — which is rather fine for OTA updates — and a high failure rate in mainland China, which is very much less fine. You can enable S3 logging to monitor and put a number on that if you’re interested.
For the world, a simple Cloudfront CDN will do magic and can likely be deployed to production in minutes. For mainland China, you’ll need a private link through the GFW which can be obtained from one of the Chinese ISPs (China Telecom, China Unicom, China Mobile), so your Chinese CDN PoPs have a reliable link to your S3 origin. Expect something in the 1-5k$/mo range for the link, and you’ll need to setup a Chinese company to obtain an ICP number. Larger CDN providers like Verizon or Akamai can likely provide a more streamlined, one-stop solution.
CDN delivery would fit very well with your Entreprise plan…
Best