Wow Arjan. That is indeed a wonderful shield.
I am soooo happy you bought it.
I thought about the missing upperpart. And I turned the question. Why is there a lower part?
I looked on old Bagobo warrior pics and the one with the shields I found were standing with the shields on the ground, leaning with one arm on the shield. I could imagine that an unequal level of the ground will be compensated with the round lower part. I will sent you some pics, cause when I make them smaller and attach them, it is hardly to see!
At the other hand I think in a fight I will better like to put my chin on a straigt upperpart than on a round upperpart, cause at the sides a little of my neck will be vunarable because of the roundings.
But both are guesses.
Maurice