In the WR he lands on flat ground after the button presses. Either just have enough speed to land on the sloped ground, or bunny onto the railing first to gain enough height to allow you to land on a slope after a press.

Do you know that he lands on the railing right ? It's pixel-perfect bu he does, that's why he conserves speed and not loses some ups by landing in a flat plane.

Don't forget that the WR has tens of thousands of tries, he routed single pixel of E1M1