How does one determine the sett size for a tartan and can it be adjusted and still maintain the proper proportions?

When I look at a couple tartans in particular, the pictures appear to show the 16oz version having a larger sett than the 13oz version. I imagine that is due in part to the thickness of the wool threads...

My concern is the tartan I am really hoping to have a kilt made with appears to have really small sett from the Scottish Register of Tartans (http://www.tartanregister.gov.uk/tar....aspx?ref=5384). I am afraid it would look too small and busy on a kilt. The problem is, it is not listed as a stock tartan anywhere so I can not get an image to compare (like the 13 v. 16 oz comparison I refer to above on other tartans). The only images I have seen of this tartan are on scarfs--and therefore are naturally smaller setts, but it's hard for me to imagine a kilt in that small a sett.

So, what determines the tartan? The thread-count or the sett size or both? Can I request that the tartan be woven with double the count--thereby keeping the same ratio but also enlarging the sett? Would this even work or alter the appearance too much to make it recognizable?

Ultimately, I sense that I will be paying for a custom run on a tartan. Then, of course, having a premium well made kilt to my measures. I really do not want to spend $600-$700 (or more) on a kilt just to have it arrive and be disappointed due to the size of the sett.