From what I understand, the difference between a normal wave and a tsunami is not the height, but the length. To compare, a wave of the height that devistated indonesia a few years back is only about 100 to 150 feet long, whereas that tsunami was something like 4 miles long. It's not so much that the wave hits the shore, but that it keeps coming, and coming, and coming...
Also, the injuries and fatalities are not caused by being in the water (most people can tread water or swim for quite some time), but by being slammed into other objects, or crushed between debris and stationary objects, or by being held under.
If I was offshore, I would try to stay there, and plan to try to get around to the back side of something solid when I was carried ashore. If I was on the beach, I would go up or in or both.
The hotel across the street from my house is a tsunami refuge assemblly area,so I guess I'm OK. -N