In Efficiency mode the e-tron will be at height 2/5. When traveling at highway speeds the car will then lower to 1/5. I have not confirmed if this is how Dynamic works as well, but I almost always use Efficiency and whenever I have checked the height > 60 mph it is in 1/5.
My guess for the "bowing" is possibly that if you are on a highway with traffic lights or similar (we have some in rural WA state) and you quickly come to a stop, the car is adjusting to the lower speed by going from height 1 to 2. Once you accelerate back to highway speed the car lowers again, but you don't feel it with the road noise, etc.