findOne hook not triggered for relations

I am using the strapi aws s3 plugin to upload media files to S3, but would like the assets to be served over a CDN. The S3 bucket itself is private. The strapi aws plugin uploads data to s3 buckets and also stores the url for the media with the bucket uri. I need to replace the domain in the url with the cdn one in order to see the media.

I can easily do this for the API by modifying the controllers, but I also need to do it for all the controllers used by Strapi Admin otherwise all the media shows up as broken links. I thought I could use content-type hooks to format the data, but they don’t seem to be triggered from relations. (The upload plugin as i understand is one-way related by the collection with media type attributes).

Would appreciate any help on how to proceed. Many thanks!