Banded Mail is not even better than Breastplate and thus it is not a good choice. Banded Mail has a total of +8 (AC+max dex) while Breastplate is a total of +9 (AC +max dex).
You cannot talk about optimizing armor without discussing what quality you are optimizing for. Nowhere in your post or in your webpage did I see that you were optimizing for ACP rather than AC although it is possible I missed it. Now that is clear.
Frankly, people see optimizing armor and most of them will try to optimize the protection without sacrificing whatever they feel they need. For some that will be ACP and Speed.
In any case no regression is required for Armor Class Bonus and Dex bonus. It doesn't matter what your Dex bonus is since at any Dex bonus below +9 the best armor (for AC purposes) is going to be Full Plate.
You are really over-complicating what is a basic concept.