However, having the Completion radius set to 6 does still work on my end. You just need to fly low enough and close enough for the attaching sequence to initiate. Then you need to wait for it to finish before taking off again. Setting the Completion radius to 0 meant you could pick it up from higher and further away. The 6 in this case means 6 meters from the crate to the center of your helicopter. Hope that helps!