The directivity of the 807 Erin reviewed didn't seem terrible. Definitely some issues around 400-500hz (port resonance??) and then what seems to be the crossover area around 3,000hz. Outside of that though, fairly flat and/or a fairly constant rise. I've definitely seen worse directivity from speakers you and others have measured.
That speaker is garbage, man. Garbage.
Directivity aside, to smooth out the on-axis response you'll need to cut 100Hz by about 5dB with a pretty wide Q (which will effect the LF as well) and probably still need a shelf filter below 200Hz. Then you'll need a good shelf >500Hz. And once you've done that (assuming it's reasonably linear) you're at about 80dB @ 2.83v/1m. Bleh.