'still less' vs 'still more'

As per the OED definition you provided, the idiom "still less" is not referring to physical measurements, but rather it refers to issues of appropriateness, ethics, morality, and so on.

So in the discussion of the legal decision, the use of "still less" would not change whether the large measurements or the small measurements were put first. The point is not the sizes, it's that the mis-measured products were unacceptable and a breach of contract.

As an additional (and maybe clearer) example of usage, one could say:

It's bad enough that you overcharged a customer for the items they bought -- still less should you have done it when the customer was your own mother!

The phrase "still more" is also common in English, but it is used as a synonym for "further."

https://www.macmillandictionary.com/us/dictionary/american/still-more-further

still more / further

used for emphasizing that an amount, increase, reduction, etc. is even more than the amount already mentioned.

Fuel prices could rise still more in the coming months.