Similar to my reasons for moving on from my Acme cabs, but in the spirit of this thread, the 10" drivers of the Acme extend WAY lower than the 15 driver you are using, much less that 15" driver in that tiny little box.
Agreed though, my little Bag End 15 (pretty similar to your cab) always sounded much better 'on the gig' to me for my playing style and tone goal than my B210... but it surely didn't 'go lower because it was a larger driver'.
Yes, the Acme drivers extend lower on paper but I found that extension didn't translate to any improvement in lowend on stage. I don't really care about specs. I'm more interested in practical use.