Unfortunately the estimates are just their averages. So many things can come into factor that make it very difficult to say your plant will be this high and this wide accurately. I have had autos that claimed 36 inches tall, and they have far exceeded that height. There are LST techniques you can do to keep your plant short and bushy. Or things that can be done to make it less bushy. I hate to say this, but it is a crap shoot trying to guess a plants size, you never know until it grows... I have a white widdow growing that was supposed to be an auto... She is 7 foot tall and wide... How big of a space do you have to work with?