User blog comment:Xilinoc/Ch. 618 - The Dark Arm/@comment-2211792-20150309051438/@comment-26091912-20150309124007

It could just be that Aizen's reiatsu is confined closer to him, making it a lot more concentrated.

Back when Urahara's seal took effect, Aizen himself stated that the power he gained was disappearing. Also, if he still retained that power after the fact, how was he restrained in the first place? Did the Central 46/Kido Corps know they couldn't touch him, but then forgot?