I wish I had seen this when you posted this, because I was doing about the same thing at the time.
My set up was different, using larger versions of the WO.
WO for PA in a small club, small band with some DSP equipment, though, very similar. For future reference, here's what I discovered.

The graph on the DSP gear was showing a displacement correction for the WO at 26" to 32" and it surprised me at first. It was dependant upon where the mid bass horns were positioned, of course.
The sound was better with the midbass cabs all the way to the back of the WO cabs, offering a "platform" for the midbass to radiate more effectively. So, 32" for a 4x4 WO. That's not a typo, but a larger WO configuration, using 18" drivers.
After I tried a tape measure, the tape was more like 46" to 52" so the "rubber mouth'' thing you mention which Steve speaks of, is real again.

I came to realize that the DSP was sensing the output of the front chamber port which feeds the horn-like output structure of the cabinet.

It took me a minute, but the DSP analysis took into account only the offset of the waveforms it was measuring and comparing without regard for the actual physical location of the eminating source or voice coils. The machine considered the exit port from the front chamber to be the "source" of the wave form.

The position of the voice coils was irrelevant to the measurements.
With my 4'x4' dual 18" WOs, the offset to the midbass horns was less than I expected by almost half.
It worked great!!

I was using the cheapest Dayton $150/when you buy four drivers with usable specs. There were cheaper Goldstar and Pyle versions, but the Daytons spec'ed out better for an extra $30 bucks a pop.

They weighed about 250lbs (added some bracing), but that paired with a 1KW amp and you have some fairly cheap and respectable club bass sounds at half the cost of anything even marginally comparable.

There was one band that only wanted one and already had an old Peavey amp (so they were on the super cheap plan) about 200W/C and they said that was all the bass they would ever need.