I don't have a crazy amount of experience but I think if you actually got 3lb dried off 9 plants, you did fucking great. Are you sure thats right? That's 1344grams/square meter or 5.3oz per "overcrowded" plant. That sounds very very high. Like I said, I'm no expert but I think cutting down to 2 plants you are highly unlikely to get 1.5lb per plant... Even 4 plants I think would have to veg quite a while to get 12oz. per plant. If you are going for weight and getting 3lb per cycle in a 3x3, I say keep doing what your doing. I am sure others will offer advice, some even good advice but I have not seen any grows pulling 3lb in a 3x3 with 2-4 plants or even 9 for that matter. I'm not saying it's impossible, just unlikely. Sorry for my sceptisism but 3lb is an incredible amount of flower for a 3x3 space no matter how many plants, what lights or even running co2.