The fact is, if you're in stealth you can actually aggro the boss earlier than other people out of stealth, even if you're standing at the same distance.
I could be 5 feet behind you and aggro the boss before you if I was in stealth.
Yes you do, this is why you have to stand farther back before combat in stealth, you have to be aprox. 15m away from your group if your group is 15m from the boss. If you do see the target for whatever reason you are too close so pop out of stealth, you won't aggro, run back farther and restealth and you should be fine.