You refer to 10 excavation maps.
How many excavation destinations maps you get out of those 10 maps?
It is essential to fly more planes of the same type at the same time to excavation destinations (that is, to complete flights only after all of them have landed). Flying 6-7 of them I almost always got 2-3 map chests without any bonuses activated. Up to now it only happened one time that I got nothing.