Board Thread:Improvements and Issues/@comment-15519592-20130817040010/@comment-15519592-20130817041846

Yeah, they all have that, but the Captains far surpass Ichigo's friends and THEY could not feel Aizen any more.

Now I have to go look it up again and see if Aizen did mention he had dropped his power, which would, theoretical if he lowered it enough, let others feel him, or if Tatsuki didn't notice Aizen before Aizen noticed them. I just remember being shocked she could feel his power when the captains couldn't. I'll get back to you once I find the right volume on the shelf, as it's faster than digging through anime episodes.