I think you're doing good if you're planting a 1-2ft tall clone in mid-June and end up with a 6ft tall plant. If you want bigger, then get that clone 1-2ft tall in mid-May. And of course whatever you're using for a container plays a role. Digging out the ground and filling in with nice soil is best. Beds are good. Fabric pots are good too as long as the roots can get through. You can undersize the container, but you'll have to increase your schedule to keep it growing. I grew some 5-6ft tall plants in 20g pots, which is really like 4-5ft tall plants, but I they needed either water/tea/feed literally everyday.