Actually is pretty common to spawn and boom, surprise, you have an enemy tiger 1000 yards at your back. Make the spawn point dynamic, so they retreat with the presence of enemy ground forces, or do not allow GVs to aproach at less than X yards from the enemy spawn point. Personally I prefer the first option. For example, spawning at the first point of the line (spawn arrow) which range to any enemy GV is larger than X yards but closer to the original spawn point.