making an aspis

[PMBardunias]

I disagree. The angle of presentation when in use of this part of the shield, must necessarily extend the thickness a weapon must penetrate, thereby allowing it to be thinner in construction, but still present the same effective thickness to a weapon.

I see what you are getting at and the effect could be useful were it not for the fact that the large off-set rim already covers a blow that would impact on the truly narrow band of shield that is bending out near the rim (I should note here that many vases show a much more gradual domed shape than we generally ascribe to the aspis. In these cases they could gain from the sloped effect.) In general I am comparing the aspis to shields such as the Khalkan which is almost conical and seems to be designed to stop arrows from penetrating.

There are in fact two different, but related effects involved. In the first, which is analogous to sloped armor on tanks, any deviation from perpendicular for an incoming stab increases the thickness of wood it must penetrate (at the extreme when parallel to the shield it must penetrate the whole plank!)

The second advantage comes from intercepting an oncoming slash with the greatest surface area of wood. Simply put the best way to stop a hacking attack is to have it impact perpendicular to the flat front of the shield. The important thing is to maximize the area of the weapon that impacts the shield at the same time. This force distribution concept is what allows us to ski. Weapons get around this by making their striking surfaces more narror- a war-pick as opposed to a broad-axe. A curved shield may be angled in a manner that intercepts incoming blows with a flatter surface when the ability of a warrior to present the flat reliable might be limited.

...I take it, since you don't have access to Blyth's original report, that it is given as a reference/bibliography by Sekunda?

Yes, it would be good to find someone with acess to this report. Without it I am forced to trust those who appear to have read it.