Board Thread:Versus Debates/@comment-26037879-20170601032009/@comment-30323490-20170601102824

Quote from the wikia: "This aura can act as an extension of their body and cannot be seen by anyone other than those who have trained in senjutsu..." "Only users of Sage Mode can see or sense this aura's extension"

So even if the enemy would be aware of the NY extension, it would still be pointless since (unless they have senjutsu training) it would be impossible to sense or see it.