I've been searching for the Rokubi for months, and the Gedo Mazo for years. That doesn't give me the right to automatically know their exact/general area and location. Unless of course I've actually gathered enough clues, hints and overall information to find them. (Not that I really care about them anymore.) And I've been a Perfect Sage Mode user for a while now, and I'm pretty sure that Sage Mode doesn't necessarily allow you to sense somebody kilometers, or even countries, away. Otherwise, I would have found all the Tailed Beasts, the Gedo Mazo, created the Jubi, split it, redistribute the Yang halves back to their owners and keep the Yin half for myself, and then just sit around in a newly assembled throne in my village for the sole purpose of just sitting there and watching over the land.
But about the argument for Kay's barrier. If she hasn't put it up yet, but is simply explaining it's history and certain notable figures who have experienced and accepted it's use, then it is more than obvious that she is going to decide to put it up next post. Either way, you can't stop that if you just entered the general zone. Not even claiming metagaming would stop it, since she already had intentions to put it up.