TL;DR: Enchanted gear that improves the %success of your sneak actually decreases your chance to sneak.
I don't know if there is other math involved, for example, does this affect characters with very low level sneak skill (and no perks?) All I know that's true is with my character-level 49, fully sneak perked / skill-capped thief, this absolutely holds true. It is also possible that this is always true, but only so noticeable at higher levels as in my case. Here's a recap of the testing I did for the previous thread.
With Sneak gear equipped (+160% Sneak Success)
- Exit Keep by entering the door
- Loads into the outdoors
- The eyeball sneak indicator immediately opens to detected and the Forsworn engage combat
No +Sneak gear equipped
- Exit Keep by entering the door
- Loads into the outdoors
- The eyeball sneak indicator remains perfectly closed
- I remain still for 10 seconds, still no blip on the eyeball
- I stare directly at the Forsworn, staring directly back at me
- I walk slowly to the Forsworn and stop maybe 10 yards from them
- Sneak indicator remains flat, no detection, not even searching
- As I get up close enough to touch them while facing me, they finally engage
So that settles it - The sneak gear decreases my ability to sneak effectively. I am near virtually unseen without it, and I'm useless with it. That's a pretty sharp contrast!
I should note, I have not installed patched 1.2, in fear of the issues I've read it can cause. : ) Other than this possibility of course. If anyone has 1.2 and is willing to test this out, it would be cool to have that here.