The image below is CE 543. It is difficult for me to tell from the photo, but if the lip is flared out it isn’t by much. The yellow circle is a round circle approximately the size of the mouth of the shell. The blue circle depicts an arc at a similar radius as the outside of the bridge on the rifle. The edge of the bridge could have made that dent in my opinion.

No, It doesn't have to be much. It is a shell not an anvil. Somebody here suggested it was a stake mark. Maybe check that out.
I thought you liked AI? You don't believe what it produced?
The bridge can cause a dimple in the center of the dent?