Inductive reactance is a function of current and voltage (and distance and time...) applied to the voice coil. Rise and dip are caused by excursion since excursion changes the applied field strength of the motor structure (via movement and static position in the motor field). As an additional note of interest, I have not researched time (period) as a function of waveform (sine vs square) with fixed power but I suspect it may have further implications on impedance curves.
Frequency can apply an additional resonant (harmonic) waveform and it is heard (and can be measured) as distortion in actual output. The inductive load that harmonics apply to the coil are actually rather small. At and above the tuning frequency of the enclosure they exist because the helmholtz effect acts as a spring to keep the coil in a normal flux of movement in the magnetic field provided by the motor. Once you get below the tuning frequency of the enclosure excursion increases which allows the field to weaken thanks to the coil leaving the gap further (and for a longer time length).
Now, thats not to say what is written in the cookbook is wrong, but that current (applied) technology and theory have not progressed when talking coil-propelled drivers.
The guy I mentioned earlier (Forevrbumpn) has built some really neat prototypes though..http://www.youtube.com/watch?v=rmRYTQAS7W4
edit - interesting thought, aluminum inductiveness by movement..
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