Really, for a TDR to work properly it needs to be a proper transmission line of some sort, and you usually try to match the pulse generator into the characteristic impedance of the line.
That way you get a reasonable amount of pulsed energy transmitted into the line, and the reflected pulse is totally absorbed by the generator. That is important so you don't get another unwanted reflection from the source.
The reflection you see will be the amount of energy returned, which will be almost all of it, if the far end is shorted or open circuit. How much less depends on transmission line attenuation both ways.
It certainly does work, and I once caught a government agency tapping my home telephone line, believe it or not.
That was many years ago, and it is all now a bit of a well appreciated joke, because I now have personal friends that used to work for that very same agency as electronics engineers back in those days. They remember that incident very well, it actually caused quite a stir, and I caught them red handed back then, ha-ha-ha.
The infamous Warpspeed strikes again.