It seems that I've had multiple encounters, where I'm sneaking and the bandits/thugs/ect are looking directly at me, yet don't see me (they aren't looking for me currently, so I'm hidden). I can then use my power attack (sometimes while in front of them, I'm hugging a wall) for the 15x bonus. This is when they are patrolling and randomly walk up to my character without noticing him.

It feels kind of cheap that they don't find me when I'm right under their nose.

(My character is almost 20, so I'm not sure if it's the same later in the game.)

If anything thing later in the game it will only get worse as your sneaking levels even higher. I'm pretty sure the AI/detection capabilties of enemies doesn't change as you level. This same type of thing was in Oblivion...once you are high enough in sneak people just essentially become blind.

And in MW
Once you achieve a certain (not particularly high level, around 50 in MW) you bcome vertually undetectable