Incidentally, demand load is how much amps you run on average over a 8 hour day for example.
Connected load is the load with everything on at the same time which is just an mathematical exercise and not reality.
Are you sure your average amps will be 1083 amps? I am doubting it. Also, your 1200 amp breaker is likely a 80% breaker which means that it will trip over 960 amps within an hour or two....or less. It will not trip right away. It will just trip when it gets too hot similar to your wires getting too hot.
Also, why are you using 2% voltage drop? Why can't it be 5% voltage drop? A 480 Volt system feeds 460 Volt loads, that's a more than acceptable 5%. 240V panel feeds 230V loads, again 5% voltage drop. Take a 110V receptacle fed by a 120V panel. That's 9% voltage drop and everything is just fine. Not sure what 208V loads are, but the point is that everything is built for voltage drop since most loads are some distance away.
If you really have a demand load of 1082 (again, I doubt), use a voltage drop calculator to figure your voltage drop. You may want to upsize a hair over 350 MCM using my 5% figure, but again, that breaker is going to trip a few times a day if you really have the 1082 A demand load. Which essentially means that (4 conduits) 350 MCM should work fine and meets code.