"Properly size image" report is too strict?

Summary

Hi !

I am trying to get rid of the "Properly image size" but I am facing a wall here. Here are the kind of errors I get:

After checking, it appears that I serve a 800px image, the actual displayed size is 362px and as the DPI is 2, so to serve a perfect image I would need to serve 362x2 = 724px images. But as the design is fluid, it depends of course of the screen width.

In my srcset, I have images that range from 300px to 1000px by increment of 100px. The issue is that it seems the tolerance is super small, and I would need to serve much more images (maybe by increment of 20 or 30px) ?

I have two problems with that:

• The document size would grow quite a lot (especially on product listing pages where I can have up to 50 products, so adding that many srcset will likely outgrows the minor win you can have at serving an exact size.
• This will make a pretty poor usage of CDN: we are using Shopify to serve image, and whenever you ask for a given size, it generates on the fly a new copy at each edges. This initial resize can take a bit of time (especially if the original image is super large) which means that by having way too many srcset, a lot more of users will face the initial resizing, and the cache will fill much faster and therefore lead again to more resizing.

I would like to know what is the recommended practice here, and if being too strict here actually does not encourage a bad practice that would like to extremely large document size, and poor usage of CDN.

Thanks :)