When you consider even an R22 has to chuck half a ton of air downwards to remain airborne in the hover, add in some wind and the downwash will be off on a journey of its own. Big problem for nasty buzzy windy fixed wing things who are confined to running up and down in a straight line to take off . . .
It's incumbent on the helicopter pilot to consider this, and on the fixed wing pilot to account for those helicopter pilots who don't. There was a fatal accident at Oxford some years ago, caused by the downwash of an S61 overturning a Warrior on short finals, and a helicopter downwash may have distracted the 172 pilot who crashed at St Mawgan last year.
QDM - if you're even up in my neck of the woods drop me a line and we'll have soooo much fun with our clothes on.