Based on my recurve experience.
There is often little relevance of the distance. If you're looking for greater helical rotation, you're better off using spinning fletches or even angling your fletches to get it to rotate more.
The biggest factor in the distance between the nock and fletching for olympic recurve, is very simply contact. Due to the effect of the Archer's Paradox, the arrow would flex one way, then the other as it leaves the bow due to imperfections of release. It is this effect that MAY cause the fletch to contact with the riser. Contact would cause two problems, a broken/damaged fletch (not something you'd want) and inconsistencies in your resulting shot. To avoid this, the fletching could be placed further up or down the shaft to avoid contact.