When killing Dragons and NPC's, how do I get a better kill scene? Like when you jump on top of the Dragon's head and slash/ stab it?

There's a perk that gives a chance of beheading an opponent.

This may just be coincidence but I've found pressing forward and attack at the same time helps increase the chance of it happening. I ran through a bandit cave to test out this theory and I got a beheading about 8 out of 11 times, so I went on my noob account that has almost no perks (Level 7) and the same thing happened. Like I said it may just be a coincidence. (I'm on PS3 if it makes a difference)