Edge Glitch on Chamber 18

[AtomicThumbs]

I'm trying to use the edge glitch technique in this video to do the challenges on chamber 18 but in 30 minutes of trying I've only been able to get it to work once.

https://www.youtube.com/watch?v=qb3mVgZP9Jw

I place the blue portal and then the orange portal but when I walk up to the wall to place the glitch blue portal it won't let me do it.