I've been having similar problems; I'm guessing we're going to the same lhbs. I think i have it narrowed down to the fineness of the crush, and am hoping to solve that with my own mill. If that doesn't work, i'll have to think of something else...
Apparently I can't quite figure out how to post pictures, but here's a link:
http://www.flickr.com/photos/58989229@N06/
I can get four Cornies in there, plus the CO2 with some room left over for some loose bottles. It's a little taller than I was originally shooting for, but I'm not complaining...