Each fall we recapture lost teeing ground. During the course of a season or two the tee edges move slowly inward from routine mowing. A cautious mower operator will error on the side of not scalping the edges, always cutting just a little bit on the inside edge of the tee perimeter. Over time, the tees become smaller.
So we cut back to the original edge in cooler weather when scalped turf recovers easily. Some tees are more pronounced than others, but that is why you are seeing scalped edges on tees .... it's intentional.