The short form in my head relies on dividers.

Lets say its a 100 ohm 5V step,

While traversing the 100 ohm line its a voltage divider at 2.5V. The wire acts as a 100 ohm load.

once it reaches the termination resistor or impedance change, the divider is altered,

So lets say at the end of your line you had a 200 ohm termination, and your measuring right at the signal source,

Your signal begins down the transmission line, loading the generator with an ideal 100 ohms, resulting in 2.5V, On the oscilloscope this will be what appears as the first bump,

Once the signal reaches the 200 ohm termination, the divider changes, and you get 3.33V, but you dont see this on the scope yet, it still has to go back along the transmission line to your measuring point,

Then once it reaches back, you see the second bump to 3.33V and is steady until the next change,

the same holds true for a 50 ohm termination, you see the 2.5V until it reaches and returns from the termination, at which point it shows a negative jump to 1.25V,

Now in your example with the 100, 200, 400, etc impedance line, it gets a little weirder, lets assume all these are the same length

Your signal like the previous ones would start off at 2.5V along the 100 ohm transmission line, This is your first bump.

Once it encounters the 200 ohm impedance the divider changes, and 3.33V begins making its way back to the measuring point

The 3.33V reaches the measuring point at the same time as for the 400 ohm line, so at the measuring point it bumps to 3.33V and at the beginning of the 400 ohm it bumps to 4V.

This continues along, and you will see smaller and smaller bumps being added further and further apart, (longer time for round trip)