But the Signal client encrypts images before sending them to the Signal server. If it padded out the images at that point, the images would all be indistinguishable from each other unless Cloudflare were actually able to break the encryption (which would completely undermine the entire security model).
Ah yes, I'm sorry, I mistook the context. If Signal encrypts the images E2E, you're right that it wouldn't matter what Cloudflare does, especially if padded.