Bob, I haven't touch a real antenna for several years, and I never said I had my S4, 2 feet above the Earth.
The models I just posted is all I have that suggests my opinions on this mater. Again the model I started with above was at 8.5' feet above the Earth, and I simply raised it up to 36' feet and posted both models to compare. My models are what they are, but I did try and run the Average Gain Report in Free Space...so I have some indications that Exnec is not playing with an unreliable input of the dimensions, and the feed point is close to where it belongs for such a model, and that is according to what error checking by Eznec determines in this case.
Except for one time with my Sigma4 when the gamma match got bumped out of position directly between the two radials where it was supposed to be carefully centered...that match never changed as much as is being suggested here...as I raised the antenna over several different installations over time.
That always impressed me with my physical S4 antenna. My old Startduster use to go up and down at different heights too...and I was had a solid match too.
My old and best A99 did on occasion change upon my on raising. but I blamed that on possible radiation on the feed line and mast. I could also see it ill-effect performance and that did not make my happy.
The only thing I ever saw change noticeably was the signals at different heights.
On my AS Sigma4 I once added a choke with ferrite cores in the cylinder built for 11 meters by Palomar, with connectors on both ends, and I also made a couple of coaxial chokes. None made any difference on this antenna that I could tell.
