i would guess that you could have a deez yield on anything 18" plus.. but i dont have much experience with hash plants.. how much yield are you talking.. in ounces?
I myself would Clipp off all the Branches from the lowwer 1/4 of the plant. Then 3 days later stick it into flowering. Your plant will more then double in size by the time you harvest. You will get at least an OZ, with proper lights and Nuts.
1 ounce is entirely possible, just clear out on the bottom portion then wait a few before flowering like lord dangly said... you have a good yield by harvest time.. good size too..