I can't imagine the amount of times I have missed a one hit sneak kill due to the game going into the killcam and insisting on paralysing the target as soon as I let off the shot instead of on contact.
The perk actually sends out an invisible Paralyze spell that's faster than the arrow. So if it hits and the target doesn't resist, they're going to fall and the arrow will miss. If you want Paralyze on contact, put a Paralyze enchantment on your bow and spend that perk point elsewhere.
Hey there, sweetroll; I just cast Oakflesh... if you know what I mean.