I set the slider to 0% on Lalafell.
And actually when I put on the Edenmorn caster top- it automatically gives female Lalafells the largest breast setting which I found disturbing.
I went back with a fantasia to make sure the setting was at zero & it was- so, that falls to the armor designers.

Also, look at the recent hairstyles- they fit the look of toddlers & not adult women (I know the hairs came from a botched design contest but SE could do better to implement the vast amounts of hairstyle requests from players because of how dissatisfying the variety is)- The contest hairs don't look good on anyone except Lalafells- but the breast slider I always joked was SE's tactic at loli grooming.

The SE designers could do more to give us more mature, beautiful hairstyles for females & more masculine, short hairstyles for males
And do not design armors that give Lalafells breasts. (exceptions I could see are if it's a gladiator/ centurion breast plate which have masculine shapes)