>>>>If I read that right then my supposition was correct ? :
>>>>"Additional columns should be ordered based on their level of distinctness, that is, from the most distinct to the least distinct."
>>>
>>>In other words, from the most selective (e.g. column with many unique values) to the less selective (column with less values). This is how I understand it and this is what I said.
>>
>>You said: "If you have many categories and just few sites, then using Category as first column "
>
>Right, this is how I understand the above sentence. Are you saying that my understanding is wrong?

Seems so to me. In your example categories is the 'least distinct' but you advocate putting it before sites.....