How not to ‘Store images locally’

I have the Store images locally disabled for all the feed sources on my site, but the images are still downloaded to the /wp-content/uploads/ folders. This is not an issue for the bandwidth, because I’m using the Jetpack CDN, but it is an issue for local storage, especially since every image has a couple of variants (ie different sizes). Right now for 1200 posts there are more than 8000 images, all of them about 450MB.
So is there something else I need to do if I want images not to be stored locally, but hotlinked instead?
If it helps, for the feeds I have the Media attachments set to ‘insert at the bottom of the post, and the Post thumbnail source set to ‘generate from the first post image and Store images locally unchecked.