This should make it alot easier to understand what I am getting at.
Here you can see three plots.
The first plot (blue)(yours) starts its cutoff at about 35 Hz and has a max gain of about 2.2DB in the 62hz area with about a medium width peak. (slightly boomy in those freq.)
The second plot (yellow) is tuned a little lower in the space you got, resulting in a slightly smaller box also. you see even though it is tuned lower, 32hz, it actualy starts to cutoff before the first box. (this one is about 36.5). It has a max gain also of only about 1.6 and has a slightly wider peak, which would be slitly less boomy (though not as loud and not drop as low)
The third one is what I would idealy go for (I enjoy the more the SQ then the spl, though when I can I go for both.) This one is tuned to 31 HZ but because we also have box volume working for us its cutoff begins around 28 HZ. Its max gain is in fact only about 1.3 but has a very wide peak, so the sound will be smooth across that large elevated range, and the peak is also around 48HZ. Resulting in a box that will sound much louder in the low range bass. 12's dont have any problem in that mid range bass, so I'm not concerned there anyway. In a Ideal world, this is what I would go for.
EDIT: i realize that third box is hard to see, its 6.5 cubic feet