Peter, I cannot speak to the neodium version (4592) but I can about the 4590. The overall system Z for the combination mid and tweeter is 10 Ohms. Complex impedance of the two halves of the BMS coaxial driver (mid and tweeter):
The midrange is 10.4 Ohms at a 39 degree phase impedance, equivalent to 13.5 Ohms in parallel with 0.44 mHy.
The tweeter plot is 7.54 Ohms at a 7.55 degree phase impedance, equivalent to 7.54 Ohms in series with 26 uHy.
The 6300Hz is recommended by BMS because that is where a VERY slight peak appears in the frequency response. I chose 6K for my crossover point.
The tweeter sensitivity is seemingly just fine straight up with the mid, HOWEVER, I chose to attenuate both mid and tweeter frequencies (prior to "splitting" them up)with the same autoformer, so I have a separate tweeter crossover AFTER the attenuation.
The tweeter runs "straight" with the midrange driver once that level is set. The tweeter is not the problem, it's the midrange!
Dana M.