Looks like the die was polished stronger on that area. It creates a flat spot and it appears looking strange on coins. I've seen this on a nickel before and examined the coin in hand to see what happened. On the nickel it was to cover a clash mark:
https://www.coincommunity.com/forum...CLASH_01.jpg
https://www.coincommunity.com/forum...CLASH_02.jpg
That area behind the head is where a clash mark of the base often is left even after cleanings/polishing.

That is what I feel this is. Nice eye. I noticed it first thing when I saw it also in the image. The question I figured was on the Die Deterioration on the rim area. But I read the message and saw that you potted it as well.
https://www.coincommunity.com/forum...CLASH_01.jpg
https://www.coincommunity.com/forum...CLASH_02.jpg
That area behind the head is where a clash mark of the base often is left even after cleanings/polishing.

That is what I feel this is. Nice eye. I noticed it first thing when I saw it also in the image. The question I figured was on the Die Deterioration on the rim area. But I read the message and saw that you potted it as well.



















