And what about the performance penalty for the server to determine 2x availability for sites where only a fraction of images are available at 2x res? I'm also

And what about the performance penalty for the server to determine 2x availability for sites where only a fraction of images are available at 2x res? I'm also not sure I fully understand how we clue the server in on where to look for the 2x version of a 1x asset. In the examples given, do the 2x versions have the same filenames as the 1x versions, but they're in the 'image' directory rather than 'img'? Seems like a significant limitation to force different assets to share the same filename, if that's what's going on here.