Do remember that an offensive player with the ball isn't entitled to any space if the defender already holds it. Time and space are irrelevant
Not sure if thats applicable to your situation because I didn't quite envision your situation because of the switching of letters and such. But always good to remember.
Definetly doesn't sound like a block on B2, as you've said he established Legal Guarding position. Did A2 dribbling displace B2 at all? If not, I've got a no call.
You said no advantage gained so I think thats the right idea.
But if A2 did lower their shoulder into the torso of B2, even without displacement, you've got a PC I think. Brushing the shoulder is what it seems like though.