Q. What is the best height for my floorstanding loudspeaker tweeters?
Answer:
When a loudspeaker is designed using the D’Appolito configuration (a tweeter sitting between two woofers) it creates a larger effective woofer driver size, and they also serve to control the dispersion of the tweeter. The tweeter’s output is somewhat corralled or contained by the sound coming from the midrange drivers in a similar way to how two parallel surfaces control dispersion. This approximates to a point source transducer.
With the tweeter located above the woofers you get the larger effective woofer driver size, but you don’t get any constraint on the upward tweeter dispersion. So it should not matter if your ears are located above the central axis of the tweeter.