My name is Alex, I'm the head of technical support at RigExpert.
This is actually an interesting question.
Our engineers could not give an exact answer why the schedule in the second case behaves strangely.
I can offer to perform another experiment - to measure the parameters of the RG-8/U coax cable using the analyzer and the AntScope and AntScope2 software....
I get that reflections show up as peaks on the IR graph, is that it?
Yes, that's essentially it. Note that the reflections can be negative or positive: for example if you try it with a short at the end rather than an open you should get a negative spike in the impulse response.
Falstad makes (I think) a pretty intuitive way to demonstrate the concept: