The wave height is adjustable so both cases are possible, however, when a wave is less than 3/4" high, the value of it toward contributing any meaningful flow is pretty limited 3/4"-1" is really the ideal in terms of not stressing the tank seams too much and creating a good flow. Unless you are just after the aesthetic swaying effect of the wave, your money would be much better spent on controllable prop pumps used in a non wave mode. You also have to keep in mind that it is a rare circumstance when a wave type flow is suitable as the only flow, it lifts and suspends debris, and encourages polyp extension, but it lacks any direction so that debris needs a directional current to sweep it away, you will almost always want some prop pumps as the basis of your flow and the wave flow is just a supplement.
With a coast to coast overflow the water will simply surge in on the high end and not enter on the lower end.