I've also interpreted Aizen's inability to perceive FGT Ichigo as him basically ascending to a level beyond everyone else. Think of it as the difference between 2D and 3D. Otherwise, I wouldn't be surprised that as shinigami achieve certain ranks, they're more or less instructed to train themselves to repress their pressure for the benefit of weaker folk. Once Aizen started strutting around, he was basically in zero fucks mode.
Conversely, I wouldn't put it past early Ichigo to just be subconsciously doing it given his whole protector persona. Some still got out, though, which could've arguably contributed to the nurturing of his friends' abilities. It just wouldn't be until he was seriously fighting that it'd come out, and now that I think about it, it probably wasn't until the Byakuya fight or so where the others were even in proximity of Ichigo. And by then they'd been exposed to other captains.
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