How Axiom did it was by carefully designing for a gradual and minimal phase shift between the mid-woofer and the tweeter at the 2KHz cross-over.

I was as surprised as you about the OW. The M2OW soundstage better than the M5HP bookshelves in my living room. Imaging of the M5HP bookshelves is better (higher resolution) though. I anticipate the M5HPOW are the same in that regard and may offer the same or better soundstage than the M2OW.

I find the soundstage of all v4 bookshelf models is better when the tweeter is lower than the ears. The speakers simply disappear in this configuration and I can "hear" the soundstage behind them. It's almost as if they are projecting the sound behind them. The on-walls are a little different in this regard. The best way I can describe it, whatever they can't project behind them, they project to the sides. The effect is a huge soundstage to the boundaries of my room.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated