I tried going up to 45Hz, it makes the hump bigger quite rapidly. The green looks like a good compromise.
I'm still not clear on the effects of mismatched impedance peaks, but on the green plot they're not too different, so I assume it won't be a major problem.
I've got enough to go on with for now- fine tuning of ports won't affect the overal dimensions of the cabs. Looks like it's going to be a fun night in with the paper, pencil and calculator tonight, then a 2hr round trip to get some ply tomorrow.
the only bass in the village