I look it at it this way.
Sheen is number 1 on any selection of Hikari fish. Balance of the sheen is what sets others from the rest
How clean the shiroji is from staining, this part always tends to happens on the head.
How clean the reticulation of scales is of the asagi pattern on the back.
Pattern is last, kohak pattern would be ideal, but there are other factors that come into play to make it a piece of art work.
I can say this, it is hard to find a really nice Kujaku tosai, because really good ones standout from the rest.
I guess in difficulity it is the way of the bloodline....