But, given the nature of the order and business and market, I would accept the current adjusted realistic 900W +/-10% as "acceptable".
Keep fudging the numbers. Eventually you'll be right.
+/- 10% hashrate and +/- 10% power draw is not what they are selling. They are selling 1.2 TH/s at 600-900 watts. If they do not meet or exceed both specs, then they have failed to deliver what was ordered.
Edit: Now I see the "+/- 10% variance" fine print. At the very extreme 1080 GH/s and 990 watts is still going to be quite a stretch. Including the "600" watt quote is very deceptive.