Round vs Oval

[Conal]

I chanced upon this IV century ivory lipsanoteque with scenes from the New Testament (Museum of Brescia, Italy). It clearly shows at the same time an oval and a round late scuta, and they look as "flat" to me, even if the artist could have thickness enough to carve easily dished shields.
Surely many of you already know this piece, but I asked myself (and you) if it's a good evidence to demonstrate that in the IV century the shields could be so too.



Valete,

Is it oval or does it look so from the angle the artist carved it?