When having a sword custom made sori, just like blade length, and weight is usually determined by the swordsmans body type, reach, and martial technique.
Of course we know that the largest change in history was deep sori to shallow sori and this was mostly due to the transition from tachi to buke zukuri mountings.
So in response to your question.. my theory would be that the type and position of sori was more of a personal thing as oppose to fashion. Of course there is also the smiths/schools preference (which would lean on fashion).
Just thinking out loud here.