Not wishing to continually post on this matter but my fix has made a world of difference.
My 07 came with the official fix as per a photo posted here some time ago.
When I used the HFT the missus said "You sound a hundred miles away".
After my fix with the foam I called her from the same place at the same speed and the reaction was that I was now very clear compared to the previous attempt.
I have since used the HFT at all speeds, including some illegal ones
and I am still as clear as a bell.
As has been said, all you need is a piece of foam to close the airgap between the mic and the plastic grill. It needs to be a solid rectangle to close all the gaps.
Unlike the official fix which involves a strategy of cutting 2 small holes in their wafer thin EPT I just cut one big hole to the same total dimensions.
Fortunately the foam I used acts like velcro on the Honda EPT tape so I could position it perfectly before clipping the grill back in place.