Very useful information in this thread. I've been contemplating buying Herbies Dampers for my ARC Ref 75SE and Modwright 36.5. It's good to hear the favourable reports.
I have always believed the standard position for a damper is about 1/3 down from the top of the tube, that's any tube. It seems it's more complicated.
I do love the ARC, but it doesn't have a hewn from a billet of Aluminium
case, the top plate is pretty flimsy. When I contact Herbie for the rings, I was contemplating some Tenderfeet and a couple of Supersonic Stabilisers for the top plate. Has anyone had good or bad experiences with these. I tried HRS top plates and couldn't hear any difference. At least Herbies are reasonably priced.