Why would you top a plant to begin with, it just slows down the growth. The best thing to do is trim up the bottoms really well and force the auxins into the flowers at the top of the plant forcing higher yields from the part of the plant best able to take advantage of the light. I have never met a single professional grower (and I have been one for about twenty years now) that tops their plants. Think of it like this, would it have helped you to mature properly if say, I cut your head off when you were three or four years old? I think not. Trim the bottoms well and you will get heavier plants. There is a myth that you can produce multiple heavy colas by topping the plants. In my experience you are redistributing the top cola into several smaller ones. If you trim the bottoms properly you won't slow down growth, you can use the trimming as clones, and you force the side branches to get much, much bigger, which is really what you are trying to do.
Tl;DR You are trimming the wrong end of your plants.