We tried to look at this at the ICAR Air Commission some years ago. Might have been the 2012 Congress. Someone had a diagram that mapped the downwash for a particular type. The President of the Commission was going to seek out other such mapping so that we could examine this aspect of the rescuers' working environment in an empirical manner. I think is was found that nobody had done the work on this and mapping generally did not exist.
We have often found that the SAR market is not large enough to warrant manufacturers' efforts in certain areas (even though their marketing teams love us). However, the HEMS market these days must surely large enough to warrant work on matter like this?