I fully developed the sneaking as well, and I can sneak just in front of some NPC. They do not see me. Others seems to have an higher sneakers detection. Also are you by yourself or you have a friendly NPC with you? I am not sure how the sneaking parameters apply to the companion.
with companions you might as well not have sneak
your companions constantly detect you so you don't get sneak attack bonus on anything even if you are hidden from the enemies because you are classed as detected thats if your companion doesn't decide to run in shouting god knows what and attacking everything they see completely blowing your cover or getting in the way of the deadly bow and arrow the only "followers" i have not had issues with in the sneak field is karliah, brinyolf, and mercer frey
i tend to be by myself too i don't like followers they push you off the edge of cliffs push you into doorways then block you in because for some unknown [censored] bizarre reason the AI doesn't stop walking once it is at you!!! they compromise your sneak get you caught by being detected themselves or pushing you into view of your enemy or activate traps behind you so you get hit with the trap despite you having the perk to not trigger traps and get in the way of far to many attacks