It's a rectangle and does not go beyond the destination. So in theory if you do a circuit that includes the other side, you are into unknown territory. Ditto at the start airfield.
Activities at the aerodromes themselves, would of course be picked up. The danger is if something centred elsewhere happens to extend very close to but not actually over your start or finish points, and lies outside the rectangle you are defining with a narrow route.
The only way with a narrow route to ensure you cover that part of the circuit outside the direct line is to use start and finish points outside those aerodromes.