Outlet Condition for Wave Absorption

I am trying to modify the CaseWaves2D _Def.xml in examples/inletoutlet to reproduce this case from https://www.sciencedirect.com/science/article/pii/S0010465519300463

As detailed in the paper, I am providing external csv files for velocity and surface elevation at the inlet and the velocity at the outlet.

I have a couple of questions regarding the same.

1. When we are giving an external csv as velocity input, at what z value is the velocity being measured. i have looked at the wiki and there is no information about that
2. For the outlet, when defining the velocity, should I set the velocity to zero until the wave train from the inlet is reaching the outlet?

Please do let me know as I am unable to simulate a regular wave train passing in the domain