Check X Y Z positions according to center of both objects. Check size of both objects.
If the one expected to be inside is smaller, and it is in the same position (keeping in mind a clearance found with the difference between both object's X Y Z and Width Height Depth values), it's inside.
If the one expected to be inside is smaller, and it is in the same position (keeping in mind a clearance found with the difference between both object's X Y Z and Width Height Depth values), it's inside.