Before a tsunami the sea recedes & then there is the destructive wave.
What is the relationship between the amount the sea falls & rises? i.e. how far do you have to run before you are safe?

I think the size of the wave depends upon the angle of slope of the shore - the greater the slope the higher the wave (I think). I know when traveling along the Oregon coast (which is a hot spot for tsunamis), there are signs that post old locations of how high the water came, and also signs that point the way to escape. I'm sure you could google and find out more.

It's really a matter of topography. The shallower the water offshore, the further the sea will pull back. The height of the wave is dependent on the amount of energy dispersed at the source of the disturbance (Undersea earthquake, volcanic eruption, meteor strike). The more energy exerted or the larger the amount of water displaced, the more likely the wave will be of significant height.
When Krakatoa erupted in 1883, a ship caught in the tsunamis was later found 3 kilometers inland and about 10 meters above sea level. The size of that wave was estimated at 72 meters in height. In other parts of the Sundra Strait, the waves only reached a height of 10 or so meters. It also (the tsunami) caused a smal rise of a few inches in the Thames River in England. How far inland they reach can also be affected by what's in their paths. Forests of Coconut palms and Mangroves help to expend the energy of the waves and keep them from moving further inland.
A rule pf thumb is that if you can see the wave, it's too late to run. Climb something high and hang on.

Charly