I’ve set up a demo page with Mirage activated on the domain. As per the documentation, appending ?forcepreloadonly to the URL will only deliver degraded images.
However, I’m not able to see the degraded image. I tested from Chrome mobile user-agent and slow emulated network.
Seems like the images are just larger than they’d need to be.
Per Website Speed Test - Image Analysis Tool by Cloudinary
evgeny-1536x864.jpg is 1536x864 but could be 580x326
solen-scaled.jpg is 1707x2560 but could be 580x870
screenshot-1536x864.png is 1536x864 but could be 580x326
Mirage detects mobile and slow network conditions and loads image thumbnails initially to improve FCP, then it loads full images with JS logic. So the purpose of Mirage to improve FCP, but it loads full images anyway at the end.