You have to consider the height of the floorstander and the vibration that each speaker will introduce to the other speaker.
Height, if the floorstanders are more than 3 ft tall, the height of the BS tweeter might be too high.
If you are using the BS and the floorstander is not in use, the vibration from the active speaker will go to the passive one. It will introduce unwanted resonance that might not be audible, but will add to the coloration of the total sound of your system. This is why bookshelfs are isolated from their stands with spikes to reduce the transfer of vibration. You want to hear JUST the drivers NOT the cabinet and certainly not the other speaker working passively.
