One suggestion…

Nostr doesn't really have the idea of srcset like figure>img does in HTML. AFAIK NIP-94 doesn't really have the ability to do it either because it's one hash per event and each size of an image would have a separate hash.

But what you're doing could be modified to support the idea of srcset - so it lists all the sizes available and then the client would pic the one that's appropriate for the UI at the in the moment. It could reduce bandwidth usage by the client when multiple sizes are available.