I’ve somewhat found it depends on the target - often closer is helpful, but I’ve also had targets where I played with the coax length to get effective faults (basically the coax length can change ringing etc). I wouldn’t worry about impedance matching for this purpose either.
But you’ll get a sharper glitch if you can move closer!
FYI - JP8 also has the glitch-out signal as well on it, if you enable the “hp” glitch output:
Can be useful in case you are using HS2 for something else.