My models for both the Vector and the S4 show the feed point impedance at the very bottom of the radiator is about 22 - 27 ohms with very low reactance at resonance for 27.205 MHz.
I haven't tested an idea for making the bottom offset legs for the radial longer at the mounting hub, but IMO that could change the resistance and the reactance too. These radial mounting legs are currently about 2.5" inches long in a model I just checked.
I find the natural 50 OHM resistance tap point for both the S4 and the V4K are higher up the radiator, rather than near the bottom. My models with a physical gamma included place the gamma tap point very close to the specs for both the S4/V4K, at about <>28" inches up to the dog bone connector,
Tomorrow I will post my model with this physical gamma included. You probably haven't seen this model, however DB and I both posted such models sometime back. The difference I note in adding physical matching devices to my models show a bit more gain and some skewing of the radiation pattern. IMO, this is due to the physical matching device being added to the model. That said, they don't seem to hurt the model...if I can get it working right. In fact, I usually see an improvement in the models in spite of the possible skewing.
I'll mention another example of how adding an element to a model that actually exists on a real antenna and how adding the element can make noticable differences in pattern and performance. Did you happen to see what happened to the pattern for the Imax model...when DB and I added a 42 pF capacitor to the middle element of our Imax models a while back?
