Some of them just ring the bell and then immediately come round the back and start throwing things over the gate.
It takes me about 20 seconds to leave my garden office, skip across the garden, enter the house and answer the door.
So, I'm standing there waiting for them to come back round, or I could chase them round the side.
If they wait they could hand me the delivery, which would probably be easier than having to indicate they've left it somewhere.