I used Keith Southern's idea of modifying the arm rest. My production Impact had the new narrower armrest but, found it was still a bit too wide for my forearm. At first I used cable ties thru the strap slots to hold a piece of foam on each side of the armrest.
Then saw Keith's mod, removed the foam pieces. And proceeded with use his mod.
To clarify the mod a bit, this is how I did it.
Peeled off the Notka foam pads, which is easy to do. Screwed back together the armrests. Grabbed a couple Stanley Quick Grip clamps, with them squeezed the grip rears and front of the armrest in to proper position. Using a smaller scrapbooking hobby heat gun,
slowly heated up the plastic from the inside a bit higher than where the bend starts near the armrest bottoms. Let the armrest cool down, removed the clamps, test fitted. Night and day difference. When I was satisfied with the new shape, I re-applied the Notka foam pads. Then put the mod'd armrest back on the Impact.
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Update:
Just took a couple pictures of it modified mounted on the Impact.
Another picture showing the clamps attached to give you an idea how I used them.
Please note the armrest was removed from the detector for modifying before the clamps were attached and heat applied to soften the plastic so it bends.
I used the front clamp to squeeze a bit more than the rear clamps. So that the armrest will have a natural taper like the forearm has.