Try bending it on a flower-pot, some of those have both vertical and horizontal curvature, like the Jango shoulders. Just like this one, but try to get a bigger one:
It's slight, but it does curve in both directions.
The best thing you can do is get hold of all the good JF images (I assume you already have) and look at the light reflection of all the Armour panels. You will soon grasp the angles/curves of the armour.
I'm working with 2mm alloy aswell for my armour, so far I have the collar, chest pieces and shoulders done. I was lucky enough to have found a round piece of pvc at work that was machined on a lathe, it's 25mm thick and about 200mm round. I've set this up in a vice and beaten/bent the armour over it with a ball pen hammer and rubber mallet.
I bent the shoulder bell plates over a large bore metal pipe, and I am happy with the results.
Any ideas on how I should go about bending the Collar Plate?
I have finished bending my Armor Plates!
nice job there! can't wait to see it on the vest and everything.