The config files contain all possible ground objects. Only those that might reasonably be encountered are included. That parameter is the distance outside the waypoints to include objects.
I have to check the code but the fact that it is an escort mission makes me think it might be a bug. Escort missions have always been odd (read pain in the a$$) because the actions of the escorted flight mean as much or more than your flight, which means a lot of non-standard logic. If I am only considering your unit's waypoints then not enough ground objects will be included. I have to make sure that I also consider the escorted flight's waypoints in the bounding box.
