You want the mid/tweet section to be level and pointed toward your ears when sitting. Most speakers will have a sweet spot for imaging and bass response around 1 to 2ft from a back wall and you should experiment with tone controls flat to find the best location.
I imagine you got it figured out. But generally tweater at ear height as mentioned above. This is typically ~36" on average. So measure the tweeter center, down to the bottom of the speaker cabinet. Subtract that from 36 and that is aproximately how many inches tall your stands should be. If your couch is low and you tend to slouch in it then you can go shorter.