How to control "size" of area of the saved startup location

When I save my startup location the "chart" covers 30,000 Square Nautical miles. I want it to cover a much smaller area. I am in the US east coast on the Chesapeake Bay. My saved location does show up the middle of this 30,000. SNM but I have to take steps to reduce the covered area. Hope this makes sense. It's difficult to put into words.

Thanks