We have fiddled a little around with the feed point to get it close to the 50ohm match. but shifting and soldering 0.1mm steps is a bit hard . But you are absolute right on the mounting of the horizontal cable. Normally I would use a small piece of semi-rigged coax cable, but for this “see if it works” project we used what was in the junk box (the BNC chassis part). A week later we made another one for 23cm and we did use the Semi-rigged for that (because the soldering points needed to be very small).
I do have a few of those perfect match - broadband - radiation less antenna’s. The work perfect . . . for testing. But a VSWR 1:2 = 10% loss of power (the horror we do have so little)
Regarding the RG58CU . . . using that on LORA frequencies . . . I would call it natural selection. Because at 100m it will have a attenuation of aprx. 45dB. The normal RG58 has even 70dB.
Source : http://www.coaxshop.nl/rg-58-cu-coax-kabels.html
Thats one of the reasons I like to work with the Aircell 7, I could use the HyperFlex or EcoFlex cables but working with 10mm+ diameter cables is like plumbing. (but sometimes you just need it). LOL
That’s why a wrote a step about cables in this LAB https://www.thethingsnetwork.org/labs/story/simple-homemade-outdoor-868mhz-antenna-groundplane/step/step-6-cable (the RG-58 note in that step is for the normal non CU RG-58 cable).