A Castelli's are typically cut pretty euro (slim). I have a very narrow chest and I have a couple of Castelli soft shells that fit fine. My heavy Castelli winter jacket does have some room in the chest, but it's not "poofy". It may be the "non-Assos" issue of all other garments not being cut as well wrt position on the bike itself.

I'm looking at the World Cycling Production catalogue I received in the mail today and it has a lot of Assos, Castelli, Craft, and De Marchi stuff, and the only thing I see that looks "poofy" is the Craft Elite winter jacket (and, of course, a couple of the models).