Topping isn't usually recommended for most autos because of the recovery time involved. You're already working on a limited time line with the auto versus the photo period plant (which can stay in veg as long as it needs to to recover from the topping.)
Are the branches getting very spindly? What kind lights are you using and how close to you have them from the tops of the plants? How old are the ladies? What size pots? Could we get some pictures of your setup?
If you're worried about space and the girls growing too big on you, have you ever checked out LST (Low Stress Training?) Low Stress Training is when you take the main stalk and the branches and VERY GENTLY start bending them down and fastening them. This allows you to effectively train the plant where you want it to go. The reasons for doing this are several fold; in your case, it's to help manage the size of the plants. LST also helps to create a very level canopy, instead of having huge spires of buds that shoot straight up. The more horizontal and flat your canopy is, the more evenly your light can disperse over the bud sites (and not be deflected/diffused by tall branches.) LST is also great for exposing more bud sites; which means less popcorn fluff and more dense goodness all around. It's also one of the LEAST stress inducing methods out of all the training methods.
Think of a plant stalk like it's a piece of copper tubing. If you put a straight 90 degree bend in the tubing, it crimps and kinks and the inside diameter integrity is ruined. If you put a GRADUAL bend in the tubing though, you can still get your 90 degree bend while keeping the diameter of the tubing.
Plants are the same way; bend them too fast, too hard, too much, and SNAP. The trick is to go very slow and gradual; and spread it out over a few days (a little bit at a time.) It's best to have started LST when the plants are younger; but it can done at any age; just have to be a little more careful. If you DO snap a branch, don't freak out, often times you can take some tape or something to bind them together and they will regenerate the wound.
If you have any questions on LST, feel free to ask or PM myself and I will personally help you!
Hope that helps bro!
