I understand that these specific numbers were chosen because these are the numbers you can have before your avatar gets hit with a very poor ranking.
The solution I propose in this case is to have a box that can be checked off in the avatar descriptor during upload. If checked, you can set your own personal minimum and maximum size, and if either number is past the limit, you will get hit with the very poor rating no matter what size you are.
If a world enforces limits via Udon then that takes priority as is already the case.