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.

I put together a playlist of all (bar 1) easy any% IL records for easy viewing, if anyone wants to watch: https://youtube.com/playlist?list=PLeAC5RL-0KSKsybrsX3I4R21LPhMviNQl&si=GqIXamFwZADLZqj2