Looks like it's more than one thing then, Maybe use a bigger grub screw ?,
As you say, The taper is not on as far as in the photo from Ed'.
Maybe the foot piece is longer than it should be too ?, So the rubber don't go on as far as it should,
Plus your thick washer !.
I agree with Ed, It's got to feel right, Or your mind is not on the driving, Which is not good.
But your getting there !.
After following Vin' Twins for many years, You can always tell it's a Vincent, The riders legs are so far apart !!,
Looks like they are on a Horse !.
With my long legs and other problems, I much prefer rear sets.
Good Luck, Bill.
As you say, The taper is not on as far as in the photo from Ed'.
Maybe the foot piece is longer than it should be too ?, So the rubber don't go on as far as it should,
Plus your thick washer !.
I agree with Ed, It's got to feel right, Or your mind is not on the driving, Which is not good.
But your getting there !.
After following Vin' Twins for many years, You can always tell it's a Vincent, The riders legs are so far apart !!,
Looks like they are on a Horse !.
With my long legs and other problems, I much prefer rear sets.
Good Luck, Bill.