...The reason you may find so many dimension variations on the web is that folk are using different types of wire and the optimum position will be in different places.
And also because a lot of hams build antennas that aren't actually optimum because
they don't understand how their design is different from what someone else did.
They get OK performance from it, and post it on the Web as the "right" way to build
There is no "one right way" to build most antennas - you have to understand the
theory behind the design you are using to know if something needs to be changed due
to a difference in the materials, etc.
In this particular case, you probably wouldn't need the short if you were using open
wire line because the velocity factor is close to 1.0. It is a good idea with 300 ohm
ribbon cable that has a velocity factor around 0.8, but you probably could find some
sort of length adjustment that would get you close enough without it.