My trusty old HF6V on top of the appartment house where I am living
This is just to show you the outlay of the radials...
I added some toroids at the feed point and a "line isolator" between the stub and the feeder. Does it make any improvements? Really, I have no idea. Maybe the SWR is a bit more stable on 20 meter, but the main thing is that it feels better... :-)
SM6EQO
The original 75 ohm matching coax is about 3,33 meters of RG-11A/U.

After having measured the exact length of an electrical quarter wave for this particular coax cable, I have now replaced it with 3,70 meters of RG-59 manufactured by Bedea.

The result is improved SWR on 20 meters from, previously, between 1:1,5 and 1:2,0 to, with the new coax, 1:1,25.

The original matching coax seems to be a little bit short, particularly if your main interest is the CW part of the 20 meter band.
Both I and a fellow ham have noted that our Butternut verticals works very well from this part of Mölndal. The area in which I am living is called “Bifrost”. In the nearby area I formerly lived in, which is called “Solhem” I noticed the same with a Cushcraft R5.

As an experiment I put the R5 above a Fritzel 3 element 3 bander beam (at about 16 meters over ground) on the same tube as the beam. To my surprise A/B-comparisons reviled that the R5 received just as strongly, and sometimes even stronger, than the beam. Reports received when transmitting indicated the same fact. The obvious conclusion was that putting up a beam at that hight together with the mast, the rotor and the signal cable is just a waste of money. Particularly as you can put up a vertical at the same hight for a fraction of the cost.

It has long been a mystery for me why my Butternut HF6V vertical seems to work so well. Then I came across Chapter 10 - The antenna and its environment - in HF Antennas for all locations by L.A. Moxon. I also read Chapter 3 in The ARRL Antenna Book - The Effects of Ground - and in particular Chapter 3-11 – Far-Field Ground Reflections and Vertical Antennas. From this it is clear that ground conductivity is very important for far-field ground reflections from a vertical antenna. It shows that the more conductive ground you have around your qth, the stronger the ground reflections will be of the signals you are transmitting, and that this is particularly important for low angle radiation.

The whole area around my qth, to the south and to the east to as far as two kilometres, is an old sea floor that rose above the sea only a couple of thousand years ago. The ground all over the area consists of a layer of solid thick clay. The ground water level is very close to the surface; between one and one and a half meters. This give a highly conductive ground and thus an almost perfect ground reflector for a vertical antenna.