When I fetch cover art for my own personal tagging, I prefer it to have the original dimensions, not an arbitrary cropping. Your prefer something different, and that’s fine, but it’s still your preference. Uploading images edited to your personal preference to CAA also imposes your preference on others.
Cover Art Archive is first and foremost an archive, not a music tagging cover art resource. While you can (probably) never escape subjective bias (e.g., in the scanning process or white-balancing etc. pre-upload), actively adding it does seem somewhat counter-intuitive to me.
I would suggest looking into uploading originals to CAA and then uploading modified cover art images to https://fanart.tv/ (there’s a Picard plug-in for fetching from fanart.tv already, and FanArt.tv speaks MBIDs, so you’re sure the releases etc. match 1:1).
All that said, I personally don’t really care too much, as long as you also upload the original, non-squared images and make it clear (e.g., in edit notes) what’s what. 