Have you tried to train the plants? I've reduced my 1 foot plants to about 7-8 inches with just a bit of LSTing. If you're growing in a confined space LSTing or SCROGing are your only options and are a must. Topping isn't really recommended with autos unless you do it early, I'm not a fan of stressing a plant out too early though. You obviously can't super crop for the same reasons.