From a fairly recent fright I have learned to worry more about the aeroplane dropping parachutists than the parachutists themselves. I can usually work out where the free fallers are likely to be but there's no way of knowing which bit of sky the pilot who dropped them is using in the rapid descent back to pick up the next lot. It is worth doing all you can to let them know where you are, especially if you are just passing by as I was.