QDM, I had a feeling of deja-vu when I read your post! Similar thing happened to me a few weeks ago, at an airfield not far from you, when a small helicopter hover-taxied about 10 feet high very close to my a/c at the fuel pumps. One of the smallest helo's, but the downwash was still slamming the flying surfaces around. A little thought (also known as 'airmanship'?) and he could have passed well clear.
On the other hand, at North Weald Air Britain fly-in I noticed a larger rotary running up near my a/c so I made sure I was around to hold on tight as he lifted away. This time the pilot made very sure he routed well away from any parked aircraft, and hover taxied a matter of inches high until he was clear - good airmanship.
Again, not wishing to "rotor-bash", but I have personally seen several other instances recently of thoughtless rotary operations. Is awareness of the effect of downwash on light aircraft part of the H-training? Any comments from rotary pilots?
Slip
PS QDM at the stalls at various fly-ins I've been looking for but still not found a copy of Jack Parham's 'Flying for Fun' for you - are you still after a copy?