On my HF6V, it calls for a "tuning stub" of a 1/4 wavelength to tune the
antenna at 20 meters. The stub is made of 75 ohm coax, and is 11'4"
long, after which the rest of the coax to the shack is 50 ohm.

How exactly does this work? There is an explanation of sorts in the
manual, but nothing I can sink my teeth into.

One of the first things I trip over is that an 11'4" piece of 75 ohm
coax is not a quarter wave in the 20 meter band - more like 17+ MHz.

The book notes that the 20 meter portion is more like 100 ohms, and the
stub allows your rig to see 50.

If the antenna works, that's cool, but I'd sure like to know a little
more detail.

- Mike KB3EIA -