Please see this page to get an idea of mechanical construction for outdoor Franklin:Latest findings ....
I've adjusted the tap between 18mm and 28mm in 2 mm steps. The best position seems to be about 26mm but there is very little difference between any of the positions. I made a 2.5mm thick plastic template and used that to form the stub wires so they are all similarly spaced.
In your diagram above you have the stub lengths of 67mm whereas the tap length is 69mm. How important is the 67mm? My 6 element has stub lengths of 68mm but the tap is 69mm.
The 6 segment Franklin has a small range benefit (~10 nm) over the 4 segment but not as much as I expected. I'll try folding the stub wires into a circle today.