Why are tweeters so high off of the ground in many tower speakers...

Your speakers have overlapping tweeter/mid response from 2KHz to 8 KHz so ear height will dramatically alter the presentation.

Most speakers with a steep crossover can do +/- 10 degrees from mid point between mid range and tweeter without any audible change - plenty of room if you sit back a reasonable distance.

An opposite example:
 dynaudio consequence
http://elitechoice.org/wp-content/uploads/2009/08/dynaudio-consequence-ultimate-edition.jpg

This is what tilting is for. :)

You can use this to your advantage. Normally (with exceptions!) speakers are designed with the listener on tweeter axis. Some adjustment however is quite pleasant, season to taste. You can do this by either toeing in/out or tilting the speaker back and forth.

There’s no requirement that the tweeters have to point parallel to the floor, so the actual height does not matter.

There are exceptions, I _believe_ the B&W 802s measure / sound much better below and off axis than they do straight ahead, by a lot.

Some speakers are designed with the mid-woofer at ear level.

What’s important is not 100.00000% perfection, but rather, getting an image and tonal balance you personally enjoy listening to as long as possible. Listen and judge what is best for yourself.

Best,

E

Sorry, I can't answer your question,  but I can say the Artemis EOS were one of my favorite speakers I've ever owned.