Vertical grows should utilize some sort of encompassing reflector to maximize light.
If you designed it right, 2+lbs per 600 is absolutely achievable... In fact, with some training, its pretty easy.. Provided you understand your nutrient regimen and your environment is dialed..
The whole point of a vertical grow is to not have to use reflector's. The plants get all of the light straight from the bulb. Can't maximize much more than straight from the light source to the plant material....