"Jim Lux" wrote
It would be interesting to run some cases where you use "wire"
(1cm diameter conductors on your helix are pretty big... I'd try
something like 1mm (18 AWG) or maybe 2mm (12 AWG)..

Here are the base feedpoint impedances for that NEC model
of a helix for the suggested conductor diameters...

1mm = 0.12 -j 2260 ohms
2mm = 0.12 -j 2170 ohms