Metal plate beneath Linothorakes or Spolades

[immortal]

Wow. Very interesting painting. It looks to me like the artist is attempting to portray the armor as simply rolled up like a rug. This looks exactly like what it going on here. Perhaps this is how the armor was stored?

I think the armour is just shown from the side, but rendered (as with a lot of ancient art) in an odd way... I don't think you could roll up a cuirass!
Body armour appears to have been stored on a stand. I believe there are a few depictions of them displayed in this way. Some vases show them standing freely, so I would assume they were fairly ridged, or at least enough so that they could support themselves.