How high are your bookshelf speakers' tweeters off the floor?

Mine are on the higher side at about 45”. They’re sitting on spiked 24” stands.

 

Ear level (when sitting)

 

The LS50 manual specifically states a stand height range of 18" to a maximum of 24". Add another ~6" for the tweeter center and unless your listening room is setup like a traditional Japanese restaurant your ears will most likely wind up being well above tweeter height. It is because the response is smoother slightly off axis in the vertical plane. Other designs / alignments have similar recommendations.

 

Mine are at 36.5" off the ground. They sit on 24"stands.

 

I think there is definitely a general rule. Tweeters should be roughly ear high unless they are specifically augmented with something like the wave guide on the KEF Reference 1's that I used to to own. They were amazing. Tonality didn't change whether you were sitting or standing.