Very good observation Bob.
Go back to the model, go down to image #3...the close-up image of the feed point area. If you want the details in the wire descriptions also check the "Wires" report. The radiator and the mount are made up of wires 1,2,3, that being the mount, the gamma section, and the radiator. Modeling does things this way because wires can only connect at the ends.
In the wires report for 1,2,3, the dimensions can be easily determined. Check the Z column for End 1, wire 1, this is the elevation for the bottom of the mount 415.5".
Then do the same for the Z column End 2, wire 1, that is the elevation for the top of the mount 432" with the mount = 16.5" inches.
By the way, this is the feed point elevation at 36' feet for this model. Not the tap point which is 28" inches higher up the radiator.
Do the same for wire #2...432" and 460" = 28" inches.
Do the same for wire #3...460" and 778" = 318" inches.
So, the radiator is overall = 346" inches which is about 0.80% instead of 0.75%. I wasn't intending for that to happen, but I probably forgot to undo an iteration or two, trying to get this model tuned. Some of this difference from specs could be in part due to differences in tubing diameters I used during my tuning iterations. Again, it was not intended...I perfer to keep to specifications if possible.
My real S4 is overall = 329.5" = 27.46 ' feet and my antenna has dimples in the tubing that sets tube lengths from bottom to top as "fixed." Like you've suggested before, the gamma will pretty much tune, within reason, for whatever length you have set.
Tuning this model is tedious and what you might start with for length might change a bit. I also find when the gamma is getting pretty close to a really good match...that changing the length might do little to make changes unless the change was really small. IMO, at this point, the gamma controls the match at the dimensions it has at the time.
I will do more to test these ideas regarding making the S4/NV4K longer.
I hope I was clear on this.
