Eddie,
1/4wave cone version,
37mm x 965mm
33.5mm x 1245mm
30.5mm x 950mm
24mm x 950mm
20mm x 410mm
radials 13mm x 1400mm & 10mm x 48mm
diameters matter because your not modeling a dipole
The radials form transmission-lines,
the gamma section is a 2 wire transmission-line shorted at its far end,
anytime you change the spacing or diameters of the conductors in a transmission-line you change the characteristic impedance of the line,
anytime you change the spacing or diameter of the conductors within the gamma section you change the range of step up ratio for r ,
narrower spacing & thinner gamma gives a wider range of stepup,
Here's what Cebik says about NEC & gammas
"It is possible to construct a series of antenna models to serve as a surrogate for the physical antennas. However, we cannot do the job in NEC-2 or even NEC-4. As suggested in Fig. 5, the gamma assembly presents NEC with two problems. First, unless the gamma and main elements are the same diameter, we encounter angular junctions of wires with dissimilar diameters. Although NEC-4 improves on the performance of NEC-2 under these circumstances, the results are insufficiently accurate for use as a comparator to the calculated values. In addition, gamma spacing is rather narrow for most beams that use relatively fat element diameters. Under these conditions, NEC tends to yield less than precise results. The relative unreliability appears in the average gain test (AGT) scores, which generally are no better than 0.92 when a perfect score would be 1.00. Since arriving at a feedpoint impedance of 50 Ohms is critical to the comparisons, AGT values in the range of 0.92 are too far from ideal to be useful. Values of 0.98 to about 1.02 are more valuable to the task of comparison"
more on modeling gammas & using calculators
https://ea5nd.com/wp-content/uploads/2017/11/Gamma-Match.pdf
