It's generally a better idea to vertically bi-amp with one amplifier per speaker, particularly if you are using identical amplifiers rather than wanting a slightly different sound for each driver by using different amplifiers such as a tube amp for highs and a solid state amp for lows.
The lower the frequency the more power a driver requires, and not having the lower frequency drivers share an amplifier should make more power and current available to each lower frequency driver.
It also depends on the the power supply configuration. With completely separate dual mono power supplies, it will make less difference. I believe the KWA-100SE has a single transformer with dual sets of secondary windings, so even though it has separate rectifiers and capacitors for each channel, the VA rating of the primary will be shared between the channels.
But because you are bi-amping a midrange and tweeter it obviously won't make as big of a difference as if you were bi-amping a woofer and tweeter or a woofer and midrange/tweeter.
Steve