Don't think of it as a 'per-plant' goal; think of it as a 'per-watt' goal.
Ask yourself- like a mantra- is every watt I pay for going to the MOST EFFICIENT use?

The first thing that I see you could change is to redistribute some of your lighting watts.
When you plan your veg/flower lighting, think of the minimum veg watts to fill the maximum flowering room. This is widely considered to be a ratio approximately 1:3. You can take one of your MH 400 lamps and toss it in the flower area, or into ANOTHER room, where plants in early flower are placed before their final re-pot, crowded under the intense blue light, to control stretch for the 2 weeks before significant budset occurs.
I'm assuming your T5 fixture is about an equivalent to a 100w HID, just for calculations' sake. So it's 1:2.2 (low) vs 1:4.8(too high), or you could take that T5 fixture and add THAT to your mothers and drop down to far fewer watts in your clone area- a couple shop lights are ample. Or you could just add another lamp to your flower room(s) and try to get more FLOWERING watts, where your product comes from. Anyway there are plenty of ways to do it. For comparison, I run about 500w equivalent (my Hortilux 400 daylight MH is the craziest thing ever- I thought for the longest time the grow shop guy was running a freakin' K halide over his vegetable display table, lol! Efficiency, babeee!) in veg to 2400 of HPS in flower. It's not perfection, but it's getting better every time I move shit around.

Okay so now we have the light arrangement out of the way and will look at your goal, since now we have some increased efficiency ideas.

2000w HPS x 12 months x 0.5g = 12,000g = 428oz =26lb. That's all she wrote. That's assuming very high efficiency USING that light, and no problems all year. Add CO2 to that equation and bump the number up significantly.

I always assume a good solid crop failure per year (trust me it happens, maybe not all at once, but lots of things can go wrong and I like to think of a 'grow year' as more like 10 months of grow time, rather than 12, lol.

Hope that helps a smidge.