Sorry but that “old dirt airport” has paved runways and I see hangers too. The airport reminds me of Montgomery Airpark which is about seven miles from me and has the same DJI Geo map restrictions. I strongly suspect you’re within five miles of it when it restricts your flight. That would put you in the green “enhanced warning zone” area which requires self-unlock.
If you play around with the geo map linked three posts up, you might notice that the restrictions change for different DJI aircraft, which apparently is dependent on their FW. Compare P3S with P3A and Mavic Pro. It’s all a bit different. It’s also possible the maps you see there are not showing all the restrictions which will come up on Go 3 or Go 4.
A handy tool besides the skyvector chart linked above is www.vfrmap.com. It’s good for drone pilots because you can toggle between a road map and the sectional chart which is useful since we’re driving around on roads looking for a place to fly.
Good luck.