In OpenWrt there is a "Distance Optimization" field, described, "Distance to farthest network member in meters." I would guess this allows some assumptions about the raw timing of transmission through the air, which no antenna could overcome. However, since it's just called an optimization, not a security feature, I'm not sure of the actual effect. Do you know if this really changes your long-range scenario?

For my specific setup, it's something of a moot point. With my home office and router at the front of the house, a distance enough to include the back yard will also include a fair chuck of the street. It may be close enough that I'd notice the suspicious vehicle, though.