ASC recommends lining up your ear with the tweeter in your monitor, so that a level straight line could be drawn from the listener's ear, to the tweeter (or acoustic center). If you like the current placement of your monitors, just measure from floor to monitor base to determine the height of your MonitorStand.
Figuring out the height of your MonitorStand is an easy three step process.
Step one: Measure the height from your ear (while seated at the console), to the floor.
("A" shown above)
Step Two: Measure monitor height from the base to the tweeter (or acoustic center).
("B" shown above)
Step Three: Subtract "B" from "A" to get "C" which is the height for your MonitorStand.
("C" shown above)
That's all there is to it!