When mine gets too big, I just cut way back to about a foot above the soil. That stimulates good new growth, especially if you fertilize. The last time I pruned, I had 3 main stalks. I now have 4 main stalks and 4 smaller side branches and it looks great. I set it outside on the west side of my house in the summer. It really likes that. It only gets full sun for about an hour and a half around noon as there is a huge oak
tree on that side of my house.
I've never tried air layering, as I get a full sized
plant much quicker by using this method.