The heigth depends on the speakers. Some speakers sound better with the area between the tweeter/woofer amed at your ear level. You can also tilt the speakers forward to achieve this. A good way to get equal angles on both speakers is to use a laser pointer.
Speaker stand height
I have a pair of PSB Stratus Minis on their factory 25" stands, but these seem too tall for my room/listening position. My listening chair is somewhat low and laid back and this i do not want to change. So I was thinking of buying lower stands so that the speakers are closer to my ear but am worried about messing up the overal tonal balance of my PSB's. Should i Be worried about the sound changing too much with lower stands, or will it simply give me more bass and a more direct sound?
btw iv'e experimented with putting these speakers on 10" concrete blocks, with a title to compensate for the height, and this seemed to make the sound much fuller. This was many years ago though and my memory could be fooling me.