I need a trimming plan

My last grow I started 5 feminized seeds in each of two 10 gal res (6 gal water). Under 400w hps. Good, air good nutes etc etc. All 10 sprouted and flourished so I kept them all going. I was very disappointed with the yield. The quality was awesome, but the yield poor. My first thought was they didn't have enough root space, but a little over a gallon per plant should be enough to yield an ounce a plant, I would think. The total grow area is only 2 feet by 2.5 feet, so the 400w hps seemed to be very adequate lighting.

So now I'm thinking this time I will absolutely cull the two weakest plants from each res, leaving 6 instead of ten. But I want to do more which finally brings me to the point. Until now now I have been an advocate (prodded by my wife) to let them do their own thing and grow natural. If one chokes out another, fine. Now I want to do some trimming and try to maximize the 6 plants who now have 2 gal of root space each. I need a plan. Where do I trim and when? Do I try to lollipop and just keep tops? Seems extreme. Do I trim off certain branches and fan leaves down low? Which and when? I plan to go to 12/12 at about 17 or 18 days, can I trim after that? If not there won't be that much to trim before. If I could get a dry 2 oz from each plant I'd be happy as a clam.

Thanks in advance for ideas or leads!

What was your yield? I'm growing in a similar space (slightly larger -- 2.5' x 2.5') under 400w HPS. My last grow was 200g dried for 4 plants, so close to 2 zips a plant on average. This grow I have 7 plants, and know I won't get 2 zips a plant simply due to space constraints. Maybe if I had a 3'x3' tent it would be possible. With my 7 plants, I'm looking for a minimum of 1 zip per plant, but hoping for 12 oz total. I'm pretty sure I can't get any more than that in my space using 400w. I'm still working out how to maximize yield in my space, but I think that the 4 cola topping method for all plants is gonna be the best bet for me.

What are the details of the 4 cola topping method? Do you trim lower branches and fan leaves? when?