I believe the suggested height is such that your elbows are even with the handwheels on the lathe.
My only addition to the above info, is what ever height is comfortable for you to be working with.
In my case having had a broken neck and a neck fusion, I am unable to look down as easily as others. So as a result of that, I have my lathe higher , so my neck is in a less flexed position to view what I am doing. It is rare that I need to look over and behind the work piece.