img responses too large

[twhid]

Greetings all,

I'm using Fastly as my CDN and we're testing a new feature of theirs that optimizes images on the fly (more info).

I'm seeing very strange results when testing using Dulles, VA - iPhone 6 iOS 9.

The responses for the optimized images are coming back orders of magnitude larger in the WPT test than when requested via a browser or curl. For example, this image:

https://internal.1stdibscdn.com/archives...quality=60

In this test:
https://www.webpagetest.org/result/17011...view_step1

Is reported to be 552.8 KB

But looking at it in a browser (eg Chrome, Mobile Safari), it's 7KB.

I haven't been able to craft headers via curl that result in the large image.

Note that I've tried using the advanced feature "Preserve original User Agent string
Do not add PTST to the browser UA string".

I'm hoping that someone has insight on anything special that WPT is doing so that I can reproduce this result.

Thanks for any help.