Here is an informative video by GR Research on why 2 tweeters don't work. This is describing why they won't work in the same enclosure, but the same concepts translate to 2 pair of speakers, stacked.
In fact, most of the problems he talks about, get worse the further the tweeters are separated in distance.
https://www.youtube.com/watch?v=MGSfaKWcetQ
https://www.youtube.com/watch?v=0GXEine4jpg
In fact, most of the problems he talks about, get worse the further the tweeters are separated in distance.
https://www.youtube.com/watch?v=MGSfaKWcetQ
https://www.youtube.com/watch?v=0GXEine4jpg