Aspis cover.

[Giannis K. Hoplite]

The illustration that made me think the aspis cover was similar to the roman ones was this one:

I interpreted the semi circles as the parts that would fold on the back of the rim and perhaps a rope would keep them together like in your reconstruction. The hung shield i believe it's not in its cover,sice the rim is visible. Even if it is,the peculiar lines on the front i think they don't represent a carrying stripe.since that would have been in the back of the shield.

Daniyal placement of the fittings i believe is a little incorrect. I also think their rope(if you haven't replaced it) is a bit short. This may make your shield hung a bit too high and make the porpax uncomfortable. Matthew Amt in his site states that his own shield hungs nicely from its internal ropes and that unexpectedly the porpax was comfortably resting inside the curve of the back. This may mean that his is hunging lower than yours?
Khaire
Giannis