We found that 1080x1080 is the sweet spot for effort and performance within Meta Ads (Facebook & Instagram).
Targetable wants to balance the amount of complexity to our users with the benefit our users will receive. We found that Meta (Facebook) also will adjust display assets slightly based on learned performance as ads run. In this case perfect is the enemy of good.
The sweet spot we found for a minimum requirement is 1080x1080. This helps us focus on larger levers that influence ad performance that Meta (Facebook) cannot adjust for us, such as incentives, copy, targeting, and relevancy of the ad as a whole.
We do continue to monitor the current usage of our product by our users and what is important to them. Tools to help uphold brand integrity is definitely something we always consider as we continue to iterate on our product.