I'm somewhat new to surfing but am thinking this is slightly different than what you are imagining. I also know next to nothing about acoustics and wave forms.

Wouldn't the wave be the height of the tube, and the vehicle be near that same height? That way you can't "miss" the wave. Unlike surfing their is no room below the wave for the vehicle do dive and throw the surfer off, and unlike surfing , a soundwave (to my knowledge) doesn't break, so there is no tumble. If you enter at the point where you're off the back of the wave, you're positioned to be picked up by the next wave, which because your vehicle height is near equal to the height of the wave, your vehicle automatically gets pushed along.

That's how I'm visualizing it, but I could be wrong.